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500
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Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
What source started the event?
|
{
"answer_start": [],
"text": []
}
|
501
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
How was the event first detected?
|
{
"answer_start": [
2522
],
"text": [
"samples collected the day before"
]
}
|
502
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
How many people were ill?
|
{
"answer_start": [],
"text": []
}
|
503
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
How many people were hospitalized?
|
{
"answer_start": [],
"text": []
}
|
504
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
How many people were dead?
|
{
"answer_start": [],
"text": []
}
|
505
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
Which contaminants or viruses or bacteria were found?
|
{
"answer_start": [
13
],
"text": [
"Escherichia coli"
]
}
|
506
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
Which were the symptoms?
|
{
"answer_start": [],
"text": []
}
|
507
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
What did the patients have?
|
{
"answer_start": [],
"text": []
}
|
508
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
What were the first steps?
|
{
"answer_start": [
108
],
"text": [
"issued advice through mass media to boil tap water before consumption"
]
}
|
509
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
What did they do to control the problem?
|
{
"answer_start": [
3025
],
"text": [
"a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public"
]
}
|
510
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
What did the local authorities advise?
|
{
"answer_start": [],
"text": []
}
|
511
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
What were the control measures?
|
{
"answer_start": [
2732
],
"text": [
"advice for consumers to boil tap water"
]
}
|
512
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
What type of samples were examined?
|
{
"answer_start": [
46
],
"text": [
"tap water"
]
}
|
513
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
What did they test for in the samples?
|
{
"answer_start": [],
"text": []
}
|
514
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
What is the concentration of the pathogens?
|
{
"answer_start": [],
"text": []
}
|
515
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
What steps were taken to restore the problem?
|
{
"answer_start": [],
"text": []
}
|
516
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
What was done to fix the problem?
|
{
"answer_start": [],
"text": []
}
|
517
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
What could have been done to prevent the event?
|
{
"answer_start": [],
"text": []
}
|
518
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
How to prevent this?
|
{
"answer_start": [],
"text": []
}
|
519
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
What were the investigation steps?
|
{
"answer_start": [],
"text": []
}
|
520
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
What did the investigation find?
|
{
"answer_start": [],
"text": []
}
|
521
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
How was the infrastructure affected?
|
{
"answer_start": [],
"text": []
}
|
522
|
Compliance with boil water advice following a water contamination incident in the Netherlands in 2007
|
In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the company’s reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future.
Introduction
Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efî¬cient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals.
System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2].
In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the î¬nished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area.
The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3].
Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident.
Methods
A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the company’s behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes.
The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the company’s response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10.
Results
Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically signiî¬cant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1.
All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-î¬ve (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%).
Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non-affected area (2.2%). In the affected area, seven (9.3%) of the respondents had î¬rst reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self-control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company.
Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area.
Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that.
Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area.
The respondents’ compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001).
Reasons for non-compliance with the advice are given in Table 2.Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3.The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area).
Factors affecting compliance
The type of mass media from which people in the affected area found out about the advice played no signiî¬cant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely to have complied with the advice (90.9% against 79.2%) but this difference was not statistically signiî¬cant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536).
Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058).Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.
Conclusions
Since excess of standard levels of certain microorganisms such as E. coli indicate faecal contamination and the possible presence of pathogens in tap water, the time between the water sampling, water analysis and the boil water notice is essential. During this period, consumers may be exposed to tap water of unacceptable quality. The choice of mass media for broadcasting the advice is therefore believed to be an effective measure to prevent panic and to protect public health.
From this study, it can be concluded that participating consumers not only thought that they had been informed about the advice in a timely manner, but that also the response of the company to ensure the advice would reach the public had been satisfactory as well as the choice of communication channels. Thus, the incident did not lead to customers’ dissatisfaction or a degradation of the company’s image.
The sample in our study derived from a database of people who subscribed to be included in different research surveys. This could raise questions regarding the representativeness of the study population. We agree that there is a need for similar studies with samples deriving randomly from the whole population and not from potentially biased data sources. For example, 100% of the participants stated that they had been informed about the boiling water advice; however, subscribers to online databases for marketing purposes may be more likely to regularly follow the news than the general population.
In the Netherlands, boil water notices are not harmonised but are determined by the drinking water company itself. This results in different advice with respect to, for instance, boiling time. Internationally recognised guidelines, such as the World Health Organization (WHO) Guidelines for Drinking Water Quality [4], could be taken into consideration in case of similar “crises†in the future. According to data from the water company involved in our study, about thirty boil water advices are issued per year in their responsibility area (ca. 700,000 households); involving on average 100 households per time. So, the chance to receive a boil water advice is small but existing.
The inclusion of recommendations including use of water for brushing teeth, washing fruits and vegetables may also prove helpful in future advice, since it is not only consumption of water through drinking that may pose a risk to the consumer. Bathing and showering may also need to be addressed separately, as a possible link between this kind of exposure to contaminated water and itching has been described elsewhere [2]. Also, although this conclusion does not directly follow from our results, vulnerable groups should be targeted separately in the advice; elderly people and children may easily miss information disseminated through the means of mass media [5,6].
Few studies have been published on boil water notices and their results seldom reach the public. Further research would also be useful to incorporate î¬ndings from compliance studies to model health effects of drinking contaminated water during similar events.
|
What were the infrastructure complaints?
|
{
"answer_start": [],
"text": []
}
|
523
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
What happened?
|
{
"answer_start": [
192
],
"text": [
"two successive cryptosporidiosis outbreaks"
]
}
|
524
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
What was the event?
|
{
"answer_start": [
192
],
"text": [
"two successive cryptosporidiosis outbreaks"
]
}
|
525
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
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When did this happen?
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181
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"text": [
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526
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Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
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Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
When did this event start?
|
{
"answer_start": [
181
],
"text": [
"June 2017"
]
}
|
527
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
What is the date of this event?
|
{
"answer_start": [
181
],
"text": [
"June 2017"
]
}
|
528
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
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Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
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Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
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How long did the event last?
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{
"answer_start": [],
"text": []
}
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530
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Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
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Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
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In which street did this happen?
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{
"answer_start": [],
"text": []
}
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531
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Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
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Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
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Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
In which region did this happen?
|
{
"answer_start": [
305
],
"text": [
"Southwest France"
]
}
|
533
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
In which country did this happen?
|
{
"answer_start": [
315
],
"text": [
"France"
]
}
|
534
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
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Where did this happen?
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266
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535
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Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
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Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
What caused the event?
|
{
"answer_start": [
1210
],
"text": [
"The entire drinking water network was contaminated"
]
}
|
536
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
What was the cause of the event?
|
{
"answer_start": [
1210
],
"text": [
"The entire drinking water network was contaminated"
]
}
|
537
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
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Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
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Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
How was the event first detected?
|
{
"answer_start": [],
"text": []
}
|
539
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Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
How many people were ill?
|
{
"answer_start": [
752
],
"text": [
"100"
]
}
|
540
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
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Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
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Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
How many people were dead?
|
{
"answer_start": [],
"text": []
}
|
542
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
Which contaminants or viruses or bacteria were found?
|
{
"answer_start": [
121
],
"text": [
"Cryptosporidium spp."
]
}
|
543
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
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Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
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Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
What did the patients have?
|
{
"answer_start": [],
"text": []
}
|
545
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Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
What were the first steps?
|
{
"answer_start": [
505
],
"text": [
"Epidemiological, microbiological and environmental investigations"
]
}
|
546
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
What did they do to control the problem?
|
{
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18930
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"text": [
"water restrictions"
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|
547
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
What did the local authorities advise?
|
{
"answer_start": [],
"text": []
}
|
548
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
What were the control measures?
|
{
"answer_start": [
18930
],
"text": [
"water restrictions"
]
}
|
549
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
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What type of samples were examined?
|
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2651
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"text": [
"stool or water samples"
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550
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Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
What did they test for in the samples?
|
{
"answer_start": [],
"text": []
}
|
551
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Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
What is the concentration of the pathogens?
|
{
"answer_start": [],
"text": []
}
|
552
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
What steps were taken to restore the problem?
|
{
"answer_start": [
18930
],
"text": [
"water restrictions"
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|
553
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
What was done to fix the problem?
|
{
"answer_start": [
18930
],
"text": [
"water restrictions"
]
}
|
554
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
What could have been done to prevent the event?
|
{
"answer_start": [
2251
],
"text": [
"sensitive and easy-to-implement tools for parasite detection"
]
}
|
555
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
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How to prevent this?
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556
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Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
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Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
What were the investigation steps?
|
{
"answer_start": [
2044
],
"text": [
"the value of syndromic diagnosis for gastroenteritis outbreak investigation"
]
}
|
557
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
|
What did the investigation find?
|
{
"answer_start": [
2044
],
"text": [
"the value of syndromic diagnosis for gastroenteritis outbreak investigation"
]
}
|
558
|
Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
|
Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
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Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France
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Abstract
Introduction
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.
Material and methods
Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.
Results
A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.
Conclusions
After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.
Author summary
Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.
Introduction
Cryptosporidium spp. is a widely distributed zoonotic protozoan that infects the epithelial cells of the gastrointestinal tract of vertebrates. Cryptosporidiosis is endemic worldwide, mostly affecting children under the age of five in low-income countries [1,2]. Two major species affect humans: C. parvum and C. hominis [1]. Cattle are major hosts for C. parvum [3,4]. The oocyst, the infectious stage of Cryptosporidium, can survive in water and soil for many months. Infected humans and animals contaminate the environment by shedding infective oocysts in their faeces. The oocysts are able to withstand standard water treatment and the concentrations of chlorine commonly used [5]. Transmission of Cryptosporidium spp. occurs mainly indirectly through ingestion of contaminated water (e.g. drinking or recreational water) or food (e.g., raw milk) or directly through person-to-person or animal-to-person routes [6,7]. A low infective dose, 10–30 oocysts can be sufficient to cause the disease in healthy persons [8]. The incubation period is an average of seven days (from 1 to 10 days) [1]. In immunocompetent patients, prolonged watery diarrhoea (>10 days) is commonly observed, associated with other symptoms such as nausea, abdominal cramps, low-grade fever or anorexia. These gastrointestinal symptoms usually resolve spontaneously within 2–3 weeks [9]. Symptoms can be severe and life-threatening for immunocompromised individuals as well as young infants. Persistence of intestinal symptoms, after resolution of the acute stage of illness, can occur and may be indicative of post infectious irritable bowel syndrome [10]. Both innate and adaptive immune responses are involved in clearing infection in human [11]. Repeated infections could lead to partial immunity against reinfection [12].
Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. Waterborne outbreaks are reported each year in Europe and the United States [13]. Major outbreaks occurred in 1993 in Milwaukee, USA (400,000 cases), and in 2010 in Sweden (27,000 cases) [6,14,15]. In the European Union (EU) and the European Economic Area (EEA), cryptosporidiosis is a notifiable disease and surveillance data are collected through the European Surveillance System (TESSy) [13,16]. Seasonality is usually observed, with an incidence increase in April and September [13]. Notification of cryptosporidiosis is not mandatory in Austria, Denmark, France, Greece and Italy; thus, cryptosporidiosis data in Europe remain incomplete. In France, only foodborne and waterborne disease outbreaks (FBDOs) are subject to mandatory notification. Cryptosporidium spp. was involved in half of waterborne disease outbreaks investigated in France between 1998 and 2008 [17].
Cryptosporidiosis is not subject to mandatory surveillance in the French Armed Forces (FAF). On June 14th and 22nd, 2017, two successive outbreaks of acute gastroenteritis (AG) were reported to the FAF epidemiological surveillance system. They occurred in a military training camp in a rural area, near the municipality of Caylus (1,500 inhabitants), Southwest France. This camp regularly hosts groups of service members from other military units in France. These outbreaks affected two companies (A and B) of 180 individuals each, deployed from Northwest France (A then B). From January 2015 to February 2017, four other gastroenteritis outbreaks were reported in this camp, all among trainees in the days following their arrival. The previous investigations identified poor hygiene conditions during field activities as one possible explanation for these outbreaks but no causative pathogen. However, biological analyses of stools were limited to the detection of bacteria and viruses. The hypothesis of water contamination was ruled out considering baseline quality levels observed on drinking water analyses. We report the results of the epidemiological, microbiological and environmental investigations conducted in 2017.
Material and methods
Study design
In order to better assess the pathogens involved in FBDOs in the FAF, a rigorous investigation method was implemented in 2017 and applied in this study. This method was based on rapid investigations, secure human and environmental sampling, and sample analysis by expert laboratories. These investigations started as soon as a suspected FBDO was reported to the French military’s epidemiological surveillance system. This approach consisted of: i/ the collect of stool samples, immediately during primary care, from at least 5 of the most symptomatic patients; ii/ the transport of stool samples by an authorized carrier, in compliance with national and international regulations, to a military reference laboratory, for syndromic diagnosis using multiplex PCR; iii/ conducting a case-control epidemiological survey, in which the exposed military population is interviewed using a standardised questionnaire; iv/ carrying out environmental investigations by a multidisciplinary team deployed on site and including environmental sampling; v- the broad-spectrum testing of environmental samples for pathogens by reference laboratories; vi- the strain genotyping of pathogens found in stool and environmental samples by the National Reference Centre Expert Laboratory for the pathogen concerned.
Epidemiological investigations
An extended search for AG cases was made in both companies using the following definition
“Patient with diarrhoea or vomiting or abdominal pain in June 2017, and present at the military camp during the 15 days prior to symptom onsetâ€. In addition, a case-control survey was carried out among 101 members of Company B—60 cases and 41 controls—using a selfadministered questionnaire, to identify an association between the disease and food or beverages consumption since their arrival.
The investigation was also extended to the local civilian population to identify a concurrent outbreak or preceding AG clusters over the period from 2015 to 2017. To this end, drug reimbursement data associated with AG treatment were extracted from the French National Health Insurance database and a space-time detection method for cluster detection applied, as described [18,19]. Rainfall data were obtained from the Me´te´o France website (https:// meteofrance.com/climat/france/montauban). Statistical analyses were performed using R Software, version 3.4.2.
Microbiological investigations
Stool samples were collected from 14 patients, 11 and 3 in Company A and B respectively. Stool samples were collected by the medical unit of the military camp. They were stored at +2˚C—+8˚C until transport with cold chain monitoring to the Be´gin Military Teaching Hospital laboratory, Saint-Mande´, within 48 hours of collection. Syndromic multiplex molecular gastrointestinal panel (Biofire FilmArray Gastrointestinal Panel, BioMe´rieux Laboratories, https://www.biomerieux-diagnostics.com/filmarray), which tests for 22 common gastrointestinal pathogens, including bacteria, viruses and protozoa, was used for syndromic diagnosis [20], according to manufacturer’s instructions. Genomic detection of the parasite in stool was confirmed by microscopic examination under 100x magnification of the stained stool samples using the Ziehl-Neelsen method for acid-fast staining, according to the technique described by Henriksen and Pohlenz [21]. In addition, a rapid lateral flow immunoassay for direct qualitative detection of Cryptosporidium spp. antigen (Cryptosporidium Xpect, Remel, Inc) was also performed according to manufacturer’s instructions.
Environmental investigations
The military camp water network includes a water tower and a system of pipes that supply the main living area and the rustic barracks for trainees scattered around the camp (Fig 1). The camp is connected to the civilian water network, which is supplied by a groundwater catchment. The raw water is processed in a civilian water treatment plant. The treatment consists of direct sand filtration (i.e., without any pre-treatment using coagulation-flocculation process) followed by chlorination. Given the first results, which identified Cryptosporidium spp. in human stool, water samples (100 L—per sample) were collected for analysis at 10 points of the military and civilian water installations, from points of use connected to the military camp water system, including taps and the water tower, to the resource (Fig 1). The stages of collecting, transporting and storing the water samples prior to analysis were entirely managed by the laboratory in charge of water analysis, which is accredited according to the ISO 17025 standard for the performance of microbiological, physical and chemical testing on drinking water [22]. Firstly, the water samples were tested according to a program of regulatory analyses routinely carried out on the taps of the public drinking water network [23]. Details of the analytical methods used on the water samples are given in Table 1. The samples were then specifically tested for the parasites Cryptosporidium spp. and Giardia spp. using the French NF T90-455 standard method for sampling and enumeration of Cryptosporidium oocysts and Giardia cysts in water samples [24].
Corrective actions were rapidly implemented in order to reduce human exposure to Cryptosporidium spp. and to bring the production and distribution facilities of drinking water back into compliance. The main actions carried were: i/ restrictions on the use of water from the contaminated network (civilian and military populations) and implementation of a palliative supply of bottled water; ii/ installation of a temporary mobile ultrafiltration unit at the outlet of the resource treatment plant, allowing effective treatment of Cryptosporidium spp. and iii/ purging and disinfection of drinking water installations and release control analyses before lifting tap water use restrictions. At the same time a search for potential human and animal sources of contamination was carried out in order to understand and prevent further pollution of the groundwater.
Species identification and strain genotyping
Positive stool and water samples (water filtration concentrates) for parasite detection were sent to the Cryptosporidiosis National Reference Centre Expert Laboratory (CNR-LE-Cryptosporidiosis) for cryptosporidiosis analysis (Rouen University Hospital, France). DNA was extracted from samples using the QIA Amp DNA Power Fecal kit (Qiagen) according to the manufacturer’s instructions. The identification of Cryptosporidium species was performed using realtime 18S SSU rRNA PCR and confirmed by GP60 sequencing as described [25,26].
Ethical statement
Each patient received care adapted to their state of health provided by the French Armed Forces Health Service. All participants received information about the investigation and the disease, gave their consent and participated voluntarily. According to French regulations, as this was a severe outbreak with immediate public health threat, no ethical approval was required.
Results
Epidemiological investigations
The two companies arrived separately in time and were independent populations (present in the camp at two different times and without common activities). The outbreaks started a few days after their arrival (Fig 2).
One hundred cases among a total of 360 trainees were identified, 40 in Company A and 60 in Company B resulting in a global attack rate of 27.8%. There were no AG cases among the permanent support staff of the military camp. The two successive outbreaks suggested a common and persistent source of exposure. Assuming the possibility of exposure to the pathogen on arrival at the camp, the median incubation time was estimated at eight and nine days for Company A and B respectively (Fig 2). Complete clinical data were available for 87 of the 100 cases with the following symptoms reported: abdominal pain (84%), diarrhoea (68%), nausea (53%), fever or feeling feverish (46%), and vomiting (26%). Symptoms lasted about a week for most of the cases and did not result in any severe case or hospitalization.
The case-control study in Company B was not conclusive. Foods were mostly based on combat rations, which are controlled and safe ready-to-eat canned meals. No statistically significant association was found between water consumption and disease, as both cases and controls consumed tap water from the drinking water installations of the military camp during training. We did not observe a dose-effect related to the amount of water daily consumed (S1 Table).
No AG outbreak was reported by the local health authorities in June 2017, among the 1,500 civilians supplied by the same water source. In addition, retrospective analysis of drug reimbursement data from 2015 to 2017 did not identify any AG cluster.
From May 30th to June 8th, the area received 55 mm of rainfall, for a mean expected value of 65 mm for the whole of June 7.
Microbiological investigations
Cryptosporidium spp. was first identified with syndromic multiplex PCR in 91% (10/11) and 100% (3/3) of stool samples from companies A and B respectively (Table 2). The presence of Cryptosporidium spp. oocysts was confirmed by direct microscopic examination. All the isolates were identified as C. hominis subtype IbA10G2, confirming that the same strain was involved in both outbreaks. Enteropathogenic Escherichia coli, Campylobacter spp. and Clostridium difficile were also found by multiplex PCR in three stool samples and considered as pathogen carriage in this context.
Environmental investigations
Local laboratory testing confirmed the contamination of the entire water network with Cryptosporidium spp. Low (4 to 6 oocysts per 100 L) to moderate levels (330 oocysts per 100 L) of contamination were observed respectively in the taps of two dwellings and in the water tower in the military camp (Table 3, Fig 1). The highest levels of contamination (>1,000 oocysts per 100 L) were found in groundwater and in the water leaving the treatment plant. Groundwater was also contaminated with faecal bacteria and Giardia spp. Oocysts were found in the tap water of a house in the municipality (90 per 100 L), confirming the civilian population exposure. The same isolate C. hominis, subtype IbA10G2, was identified in the water samples collected on civilian and military drinking water installations and was the same as the one found in stool’s samples. Physicochemical parameters and chlorine concentration (� 0.3 mg/L in water storage facilities; � 0.1 mg/L in tap water) were within the expected range.
As soon as the positive water test results for Cryptosporidium spp. were obtained, water restrictions (a ban on use of water for drinking and food preparation) were immediately implemented in the military camp and the municipality. As an emergency measure, bottled water was distributed to the entire population (civilian and military). An additional ultrafiltration module was installed at the water treatment plant one month after the second outbreak. A reinforced water quality monitoring program was implemented, consisting in a monthly analysis for Cryptosporidium spp. and Giardia spp. on the groundwater and at the outlet of the filtration treatment. The ultrafiltration module proved immediately to be very effective, as no Cryptosporidium spp. oocyst were found in the water after treatment. The civil health authorities decided to lift the water restrictions for the civilian population, after purging and disinfecting the water supply network. The same procedures were then carried out in a second phase on the water supply network in the military camp. This water treatment was secondarily completed by an ultraviolet disinfection system.
Several activities were identified as potential sources of microbiological contamination of the ground water in and outside the military camp: wastewater treatment plant (WWTP), the lagoon and sludge spreading areas of the WWTP, the collection and disposal facilities for military dwelling wastewater, livestock grazing, livestock manure management (slurry pits, land application) and septic tanks (Fig 3). Polluting activities within the protection perimeters of the water resource were strongly restricted. The main restrictions concerned the ban on spreading sludge from the military camp’s wastewater treatment plant, restrictions on cattle grazing within the protection perimeters of the water resource and verification of the watertightness and strict monitoring of the frequency of emptying septic tanks. On the military camp, these actions were monitored by the local military command, under the technical supervision of the territorially competent army veterinary structure. The implementation of these restrictions was followed by the end of groundwater contamination. No further AG outbreak has been reported since in the FAF.
Discussion
The occurrence of gastroenteritis among trainees had become so frequent in this military camp that the French service members had named it “Caylusite†(i.e., Caylusitis in English, in reference to the municipality near the camp). After successive and unexplained AG outbreaks this investigation identified the same C. hominis IbA10G2 isolate in the stools of patients and water samples, confirming a waterborne disease outbreak. In retrospect, these results suggest that the recurrent AG outbreaks recorded in the military camp were most likely waterborne disease outbreaks and caused by the same agent. The strain identified has already been involved in several cryptosporidiosis outbreaks [14, 15, 27].
Previous hydrogeological studies showed that the natural hydrogeological protection barrier of the water resource was very permeable, due to karstic rocks with faults [28]. The groundwater quality was therefore strongly influenced by the surface water. The underlying assumptions to explain the groundwater contamination were: i/ a polluting activity on the surface and ii/ direct infiltration into the groundwater during heavy rainfall. Indeed, one week before the first outbreak in June, the area received more than half of its normal seasonal rainfall. Similar occurrences have already been observed in other karst regions [29, 30]. Multiple sources of contamination were identified, including livestock grazing on the military camp, which could act as a reservoir for C. hominis [31]. However, because the water contamination ended several weeks after the reinforcement of the protection perimeter of the water resource, this was not investigated.
In case of suspected FBDO in the French Armed Forces, epidemiological, environmental and microbiological investigations are systematically performed [32, 33]. However, the pathogen involved is rarely identified, only one out of three over the period 1999 to 2013 [34]. The limitations identified to explain these poor results were the frequent absence of stool samples from patients and the fact that the parameters tested on stool samples are mainly targeted at bacterial agents. The search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing [16]. This could explain why no causative pathogen was identified in previous outbreaks in this military camp. In order to better assess the pathogens involved in FBDO in the FAF, systematic stool sampling and multiplex PCR were implemented. Our findings validate the need for routine use of syndromic diagnosis in the investigation of AG [20]. However, multiplex PCR is very sensitive, and identification of carriage of other pathogens is possible. This highlights the importance of collecting stool samples from several patients to obtain matching results. In our study, the number of samples was limited but sufficient to conclude to an outbreak of cryptosporidiosis.
As expected, chlorination and sand filtration (cut-off threshold estimated at 10 μm) were not sufficient to effectively treat Cryptosporidium spp. (oocyst diameter is estimated to be between 3 to 5 μm) [5]. The use of an ultrafiltration process at the water treatment plant proved effective (absence of parasites), making it possible to lift the water restrictions. Regulatory analysis programs routinely implemented to monitor the quality of drinking water use for microbiological testing fecal indicator bacteria (FIB). The FIB mainly used in French regulatory surveillance programs of drinking water are E. coli and Enterococcus spp. [23]. However, these FIB do not correlate well with the presence of other pathogens like viruses and protozoa [35]. Firstly, because FIB can replicate in the environment without a host, unlike viruses or protozoa. Then, viruses and protozoa are more tolerant to chlorination than FIB. The microscopy-based reference method currently used to detect Cryptosporidium spp. in water is suboptimal because it requires a large volume of water [24]. This method of analysis cannot be used in routine to carry out drinking water quality monitoring. This should enhance developing new techniques for the detection of cryptosporidium in drinking water, in order to control of the parasite hazard at the different stages of the drinking water supply chain. Over the last few decades, various protocols based on molecular methods have been developed to improve the detection of Cryptosporidium spp. and Giardia spp. in aquatic samples. These techniques are more sensitive and would require less water sample volume than the microscopic examination [36].
The trainees passing through the military camp were probably immunologically naive against C. hominis, subtype IbA10G2. On the other hand, the civilian population of the nearby villages and the military camp permanent staff, may have been regularly exposed to the pathogen (civilian and military water facilities were supplied by the same parasite-contaminated water resource) leading to the acquisition of partial immunity [12]. This hypothesis could not be confirmed because no investigation was conducted by the civil health authorities among the population living in the Caylus area. But this would explain the absence of cases reported among them. Thus, military trainees, who were not inhabitants of the municipality of Caylus, served as sentinels, helping to highlight the contamination of civilian and military water facilities and, in retrospect, the exposure of the local civilian population to Cryptosporidium spp.
Conclusions Due to the absence of mandatory reporting, epidemiological data on cryptosporidiosis in the French general population are limited. These outbreaks focus attention on the lack of understanding of the epidemiology and prevention of this disease in France. Our study demonstrates the value of syndromic diagnosis during AG outbreak investigation. This method is now systematically used for stool testing during suspected FBDO in the FAF. Our results also highlight the importance of better assessing the microbiological risks associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection. Furthermore, this type of investigation cannot be successful without a strong and multidisciplinary collaboration involving physicians, biologists, epidemiologists, and food/water safety specialists.
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What were the infrastructure complaints?
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{
"answer_start": [],
"text": []
}
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560
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
What happened?
|
{
"answer_start": [
3
],
"text": [
"outbreak of cryptosporidiosis"
]
}
|
561
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
What was the event?
|
{
"answer_start": [
3
],
"text": [
"outbreak of cryptosporidiosis"
]
}
|
562
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
When did this happen?
|
{
"answer_start": [
108
],
"text": [
"March 2000"
]
}
|
563
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
When did this event start?
|
{
"answer_start": [
108
],
"text": [
"March 2000"
]
}
|
564
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
What is the date of this event?
|
{
"answer_start": [
3061
],
"text": [
"March 1-15, 2000"
]
}
|
565
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
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How long was the event?
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"answer_start": [],
"text": []
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566
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Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
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An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
How long did the event last?
|
{
"answer_start": [],
"text": []
}
|
567
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
In which street did this happen?
|
{
"answer_start": [],
"text": []
}
|
568
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
In which city did this happen?
|
{
"answer_start": [
56
],
"text": [
"Clitheroe"
]
}
|
569
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
In which region did this happen?
|
{
"answer_start": [
2558
],
"text": [
"Lancashire County"
]
}
|
570
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
In which region did this happen?
|
{
"answer_start": [
82
],
"text": [
"northwest England"
]
}
|
571
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
In which country did this happen?
|
{
"answer_start": [
92
],
"text": [
"England"
]
}
|
572
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
Where did this happen?
|
{
"answer_start": [
2545
],
"text": [
"Clitheroe in Lancashire County in northwest England"
]
}
|
573
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
Where did this happen?
|
{
"answer_start": [
56
],
"text": [
"Clitheroe, Lancashire, in northwest England"
]
}
|
574
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
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What caused the event?
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575
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Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
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An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
What was the cause of the event?
|
{
"answer_start": [],
"text": []
}
|
576
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
What source started the event?
|
{
"answer_start": [
495
],
"text": [
"contamination with animal feces"
]
}
|
577
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
How was the event first detected?
|
{
"answer_start": [
3111
],
"text": [
"Health Department reported nine cases of cryptosporidiosis"
]
}
|
578
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
How many people were ill?
|
{
"answer_start": [
120
],
"text": [
"Fifty-eight"
]
}
|
579
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
How many people were hospitalized?
|
{
"answer_start": [],
"text": []
}
|
580
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
How many people were dead?
|
{
"answer_start": [],
"text": []
}
|
581
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
Which contaminants or viruses or bacteria were found?
|
{
"answer_start": [
155
],
"text": [
"Cryptosporidium"
]
}
|
582
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
Which were the symptoms?
|
{
"answer_start": [
6929
],
"text": [
"diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool"
]
}
|
583
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
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What did the patients have?
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584
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Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
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An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
What were the first steps?
|
{
"answer_start": [
13370
],
"text": [
"the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed"
]
}
|
585
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
What did they do to control the problem?
|
{
"answer_start": [
13370
],
"text": [
"the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed"
]
}
|
586
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
What did the local authorities advise?
|
{
"answer_start": [],
"text": []
}
|
587
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
What were the control measures?
|
{
"answer_start": [
14974
],
"text": [
"issued a Boil Water Advisory"
]
}
|
588
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
What type of samples were examined?
|
{
"answer_start": [
9823
],
"text": [
"large-volume sample of water (1,627 L) from a pumping station"
]
}
|
589
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
What type of samples were examined?
|
{
"answer_start": [
10021
],
"text": [
"taken from a domestic tap in the water zone"
]
}
|
590
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
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What did they test for in the samples?
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{
"answer_start": [],
"text": []
}
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591
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Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
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An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
What is the concentration of the pathogens?
|
{
"answer_start": [
10333
],
"text": [
"ranging from 1 to 9/10 L"
]
}
|
592
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
What steps were taken to restore the problem?
|
{
"answer_start": [
3459
],
"text": [
"an outbreak was declared, and an outbreak control team was established"
]
}
|
593
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
What was done to fix the problem?
|
{
"answer_start": [
13370
],
"text": [
"the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed"
]
}
|
594
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
What could have been done to prevent the event?
|
{
"answer_start": [
20834
],
"text": [
"continuous monitoring in the United Kingdom, together with existing surveillance"
]
}
|
595
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
How to prevent this?
|
{
"answer_start": [
20834
],
"text": [
"continuous monitoring in the United Kingdom, together with existing surveillance"
]
}
|
596
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
What were the investigation steps?
|
{
"answer_start": [
4921
],
"text": [
"information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts"
]
}
|
597
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
What did the investigation find?
|
{
"answer_start": [],
"text": []
}
|
598
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
|
An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
|
How was the infrastructure affected?
|
{
"answer_start": [],
"text": []
}
|
599
|
Cryptosporidium Oocysts in a Water Supply Associated with a Cryptosporidiosis Outbreak
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An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.
Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is determining what concentration of oocysts in drinking water is considered safe.
In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled continuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concentration of oocysts in the water could be made.
The Outbreak
In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 1997–1999, the mean annual attack rate of laboratory-confirmed cryptosporidiosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole.
During March 1-15, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16.
Methods
Epidemiologic Investigation
Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.
Microbiologic Investigation
General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Service’s Cryptosporidium Reference Unit for genotyping.
Environmental Investigations
The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Regulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team.
The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.
After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of operational, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.
Result
Descriptive Epidemiology
Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as primary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomiting, and three (5%) blood in the stool.
Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these
had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients.
Microbiologic Testing
Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable).
Environmental Results
Water Sample Analysis
Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribution. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlorinated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks WTW was classified as being at “significant risk†from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.
The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an operational depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably during normal operation; full advantage is taken of the increase in
availability of the spring’s source after major rainfalls.
On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2).
Site Visits
The concrete casings of two of the Grindleton Springs collection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead.
Rainfall Statistics
Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 2–7.
Hydraulic Modeling
A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the reservoir operation before and during the outbreak. Initially, the first “injection†of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rainfall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on February 27 would have been effectively washed out by the time the sample was taken on March 17.
Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indicated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 2–3, after the second salt pulse (simulating the rainfall incident).
Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe population would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question.
Control Measures
At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reservoirs. The first source (Watchgate) provides up to 600 megaliters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporidiosis.
At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 17–20). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.
The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamination, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.
At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible pathway (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 µ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this reason, the boil water advisory was not reinstituted. Further flushing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.
Discussion
Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source.
This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (7–9). We suggest that this high attack rate occurred because of low immunity in the population and the probable high concentration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).
The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new contamination source and with ongoing extensive flushing operations, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased counts on March 28–31 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribution pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12).
Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified.
Monitoring water samples, particularly with 10-L smallvolume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (13–15). Currently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit currently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics modeling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.
The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporidium infection in humans, will hopefully result in a better definition of an appropriate public health standard for this organism. However, recent human studies have shown a substantial intraspecies variability in the infectivity of Cryptosporidium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the community may not be possible. Indeed, outbreaks of cryptosporidiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst count’s being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the community (20).
Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes available.
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What were the infrastructure complaints?
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{
"answer_start": [
10571
],
"text": [
"collection chambers showed signs of aging and were in a poor state of repair"
]
}
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