Cryptosporidium, or "hidden spore," is a microscopic, protozoan parasite 1/25,000 of an inch in size, capable of causing gastrointestinal disease. It is recognized as one of the 3 most common diarrhea-causing intestinal pathogens in the world. Cryptosporidiosis, the disease caused by the organism, can vary significantly from self-limiting to life-threatening, depending on the immune status of the individual. Persons with greater than 300 CD4 cells/mm3 are more likely to have self-limited disease, while those with fewer than 200 CD4 cells/mm3 almost always have persistent disease. Mortality from cryptosporidiosis approaches 80% in the immunocompromised. The current lack of a cure and standard effective treatment makes avoiding exposure to this pathogen highly desirable.
Transmission of cryptosporidium is by the oral-fecal route and occurs when the oocyst, a small hard-shelled capsule formed during one stage of the parasite's life cycle, is ingested. The oocyst is extremely tenacious, highly resistant to disinfectant and capable of living outside the host for 2-6 months in a moist environment. Symptoms of infection vary, but most commonly include abdominal cramps and diarrhea. Nausea, vomiting, malaise and low-grade fever may also be present. In the presence of HIV infection, cryptosporidiosis can become a protracted disease from which recovery may be difficult.
Recognizing the importance of reducing the risk of exposure to this disease, the Centers for Disease Control and Prevention (CDC) in September 1995 issued prevention guidelines for HIV positive individuals. These include:
* Wash hands with soap and water before eating anything, after touching children in diapers or after touching clothing, bedding or surfaces soiled by someone with diarrhea. Washing hands frequently may be the most important prevention activity. Often overlooked as a source of Cryptosporidium, garden soil may become contaminated by neighborhood pets or by farm animals in rural areas. Wear gloves while gardening and wash hands after gloves are removed. Always wash hands before preparing food. A responsible adult should supervise hand-washing in children.
* Practice safer sex. Cryptosporidium can be found on the skin in the genital area, including thighs and buttocks, of an infected person. It cannot be seen, and an infected person may be asymptomatic; therefore, safer sex practices should be strictly observed. Mouth-to-anal contact can spread cryptosporidiosis, even in the presence of meticulous hygiene. Wash hands after any sexual activity.
* Always wash hands after touching any animal. Farm animals, particularly young ones, should be considered a source of infection. Contact should be followed by careful hand washing. Most house pets are safe. Young puppies or kittens should be examined by a veterinarian for infection. An HIV positive person should avoid cleaning cat litter boxes or disposing of pet stools. If help is not available, gloves should be worn and hands washed after the gloves are removed.
* Wash and or cook all food. If safe water is a concern, wash in water that is known to be Cryptosporidium-free. Peeling fresh fruits and vegetables that will not be cooked reduces the risk of exposure, and some kinds of cooking eliminate the risk. Unless processed food has been contaminated by an infected food handler after processing, it is probably safe. Unpasteurized drinks are not safe. In 1994, 160 cases of cryptosporidiosis were reported among persons who attended an agricultural fair in Maine and drank freshly pressed, unpasteurized apple juice. Investigation revealed that the apples were collected from an orchard where calves from a neighboring farm had contaminated the ground where the apples had fallen.
* Evaluate water safety. Although the CDC does not consider it to be the primary method of cryptosporidiosis transmission, waterborne transmission has recently resulted in thousands of cases. In 1993, an outbreak of Cryptosporidium in the Milwaukee municipal water supply infected 400,000 people and killed more than 100, most of them immunocompromised individuals with HIV. This was followed by a l994 outbreak in Las Vegas which killed 19 people. Cryptosporidial outbreaks have occurred in other U.S. cities, such as Denver, and there is considerable evidence that non-epidemic transmission of Cryptosporidium through drinking water may be occurring throughout the U.S. Outbreaks have also been associated with swimming pools, wave pools and water slides, and care should be taken to not swallow water from these sources. Untreated water in rivers and lakes should be considered contaminated and also avoided.
Studies reported by the Environmental Protection Agency (EPA) indicate that Cryptosporidium oocysts are present in 65%-97% of untreated water supplies tested throughout the country. Because the parasite is highly resistant to the chemical disinfectants used in the treatment of drinking water, including bleach, filtration may play an important role in the water treatment process. Filtration systems must be scrupulously maintained and specifically designed to remove these organisms. Nevertheless, all waterborne outbreaks of cryptosporidiosis detected to date have occurred in communities where water utilities met current state and federal standards for acceptable quality of water. A filtration system was in use during both the Milwaukee and Las Vegas outbreaks. Data from these outbreaks may indicate that simply complying with existing standards is not adequate to protect individuals from waterborne cryptosporidiosis. Available information also indicates that oocysts were able to breach filters in communities where water was both disinfected and filtered.
Some communities may filter only some of the municipal drinking water. Usually this is because the source water is considered to be sufficiently guarded from contamination. San Francisco, New York, Boston, Seattle and Portland are among these cities. While small numbers of oocysts have been detected in drinking water in these cities from time to time, no designated outbreaks have been reported. Some communities use a combination of filtration, sedimentation and ozonization in an effort to reduce the presence of oocysts. Testing water for the presence of Cryptosporidium is currently a labor-intensive, hit-or-miss proposition, according to The Wall Street Journal, which recently reported on the development of new methods for detecting this parasite. First, hundreds of gallons of water must be passed through filters which collect particles of dirt and microorganisms. Then, the collected material must be stained with a dye which recognizes the oocyst and it is then examined under a microscope. This process may take several days, and results can be extremely variable from one laboratory to another. Dr. Victor Tsang, chief of the CDC Immunology Branch, is currently examining methods of identifying Cryptosporidium that are more accurate and less time-consuming. Dr. Tsang's research is challenged by federal budget uncertainties at this time.
Because the health risk associated with exposure to very small numbers of oocysts is uncertain, especially with regard to HIV positive individuals, a June 1995 CDC workshop studying these issues stopped short of making official recommendations for drinking water safety, but suggested that immunocompromised individuals take special precautions during known waterborne outbreaks or periods of "Boil Water Advisories." Many AIDS clinicians and activist groups, however, have subsequently advised HIV positive individuals to follow those precautions even in the absence of official advisories.
The number of oocysts needed to infect a healthy person has been suggested to be very small, 132 in one study of healthy volunteers. The number needed to infect an immunocompromised individual is unknown, but is suspected by some investigators to be as low as 1 oocyst.
Drinking water safety can be enhanced by boiling water, filtering water or drinking safe bottled water. Boiling water for 1 minute at sea level or 3 minutes at altitudes above 6,500 feet will kill Cryptosporidium and completely eliminate the risk of infection. Filtering water with an appropriate water treatment unit can reduce the risk of infection.
Before buying or installing a home water treatment unit, a number of factors should be considered. Not all water treatment units are effective against Cryptosporidium; in fact, most are not. CDC guidelines of September 1995 recommend only 3 categories of filters: 1) microstraining filters that can remove particles 0.1-1 micron in size, 2) units that work by reverse osmosis or 3) units that meet National Sanitation Foundation International (NSF) Standard 53 for "cyst reduction."
In the first category, the units must be labeled "absolute" 1 micron, not "nominal" 1 micron, as the second group is not standardized and may allow small particles the size of Cryptosporidium oocysts to pass through. Reverse osmosis units, the second category, work by passing water through a tightly stretched membrane. While preventing the passage of undesirable organisms, there exists the possibility of a membrane rupture, especially with changes in water pressure, which would cause release of high concentrations of captured pathogens. These units must be scrupulously maintained and carefully monitored.
In the third category are water treatment units which have been voluntarily submitted by their manufacturers for testing and certification by the NSF International. NSF is an independent organization that develops industry standards, then tests and evaluates products to determine compliance with those standards. Since there are no governmental regulations or mandatory standards for these products, NSF certification is the only currently available method for consumer guidance.
NSF certification covers many areas, including aesthetic effects and health effects. Standard 53, which covers health effects, includes 21 separate categories, of which "cyst reduction" is only one. This can be somewhat confusing, since a particular unit may be labeled as meeting Standard 53 "lead reduction" and not reduce cyst exposure adequately. Units must specifically indicate certification for "cyst reduction" to be effective against Cryptosporidium.
All units have removable filters which must be changed on a regular basis, usually dependent upon volume of water used. The CDC recommends that these filters not be handled by an immunocompromised person because they collect and concentrate potential pathogens. If someone else is not available to assist with the changing process, then gloves and a face mask should be worn.
A few cautions should be kept in mind. Because NSF certification requires ongoing, random inspection of certified products, the approved list changes regularly. It is possible that an individual may purchase a unit in August, and find that it is no longer approved in December. Some manufacturers have a longer history of continuous certification, and these should be sought out. Another caution is the following: "NSF does not assume or undertake to discharge any responsibility of the manufacturer or any other party. NSF shall not be responsible to anyone for the use of or reliance upon this standard by anyone." It should be noted that to meet the established standard, a treatment unit must be shown to reduce evidence of cysts by 99.95%.
In January 1996, 26 manufacturers had approved devices for cyst reduction. Some of these appliances are readily available from retail outlets (PUR-brand, for example, sold in many drug and department stores, has 5 models that meet NSF standards). Some manufacturers sell their products only through distributors who are available to properly install the devices. Some even provide a service for filter replacement at an additional charge (Multi-Pure Drinking Water Systems has a comprehensive package which includes initial purchase, replacement filters and installation).
All of the filters examined and certified under NSF Standard 53 are mechanical filters. Individuals who are considering the purchase of a water treatment device should contact NSF at 800-NSF-MARK for a current list of certified units.
Drinking bottled water is suggested as a possible alternative, but because no consistent standards exist in this area, the consumer must be careful to select a product that is safe. Products labeled "drinking water" may simply be local tap water in a container. According to the CDC, "the origin, microbial flora and treatment of water before it is bottled vary considerably between bottled water companies and between brands of water produced by the same company. In general, bottled water obtained from underground sources, i.e., springs or wells, is less likely to be contaminated with Cryptosporidium than bottled municipal water derived from rivers or lakes. Persons who use bottled water as an alternative to tap water that has been boiled must carefully research and choose their supplier."
Bottled water that is distilled is free of Cryptosporidium. There is currently debate over whether carbonation is capable of killing the oocyst. While some reports indicate that it is, further research is needed.
Portable water filters and purifiers are also available for travelers. Ranging in weight from 7-22 ounces, they are designed to transport water while camping, hiking or trekking, but some models may be adapted for use in a contained space such as a sink. All models claim to remove "cryptosporidia, giardia and bacteria" but, as with in-home units, there are no mandatory standards for operation of these devices. Regardless of what method of water treatment is used by an immunocompromised individual to reduce the risk of exposure to Cryptosporidium, it must be used consistently and in all cases where water is ingested, including reconstituted juices, ice cubes and brushing teeth.
Incidence and Diagnosis
The incidence of cryptosporidiosis in the HIV positive population is a subject of some controversy. While cryptosporidiosis is an AIDS-defining condition, reporting of the disease is not mandatory in all states. In California, where reporting has been required since 1989, different reporting criteria may contribute in part to the controversy over disease incidence. For example, the California Department of Health Services, Office of AIDS reports zero (0) cases of cryptosporidiosis for San Francisco County for the year 1995. However, the San Francisco Department of Public Health Seroepidemiology and Surveillance Branch reports 71 cases for the same year. The difference is that the former reports cryptosporidiosis only as an AIDS-defining condition, while the latter reports all incidences of cryptosporidiosis. These differing reporting criteria may contribute to a less than accurate perception of the frequency of this illness.
Annual data from the California Department of Public Health Division of Communicable Diseases indicate either a growth in incidence or changes in reporting criteria from 1989 to 1994 with the following figures:
1989 -- 46 cases 1990 -- 165 cases 1991 -- 210 cases 1992 -- 276 cases 1993 -- 372 cases 1994 -- 477 cases.
It is estimated by some epidemiologists that worldwide, the incidence of cryptosporidiosis in the HIV positive population may reach 50%. John Cello, MD, a gastroenterologist at the University of California/San Francisco General Hospital, believes that fully 25% of AIDS-related diarrhea is caused by Cryptosporidium. Difficulty identifying the pathogen may also be partly responsible for the controversy over reported incidence. Diagnosis is typically made by acid-fast stool staining. The fewer organisms present, the more difficult the diagnosis. Excretion of the oocyst can be intermittent and the parasite may not be present in every stool sample. A minimum of 3 separate samples is recommended. Cello advises that stool samples will identify Cryptosporidium only 75% of the time, and that a colonoscopy with intestinal biopsy is necessary to identify the remaining 25%. Cryptosporidium oocysts often "hide" in an area of the intestine called the terminal ileum. This area must be carefully examined during a colonoscopy. Use of a flexible sigmoidoscope to examine the lower portion of the intestine, a less invasive and less expensive procedure, is not as likely to result in identification of the pathogen (35-40% will be completely missed).
Cryptosporidium has only been known to cause disease in humans since 1976. Between l976 and l982, it was thought to be of only marginal importance, and this may account for a lack of investigation into treatment options. The lethal course of the disease in the presence of HIV, however, has prompted an exploration of a plethora of drugs and biological agents as potential treatments.
Standard anti-diarrheal medications, intravenous fluids, electrolyte management and oral rehydration therapy with appropriate fluids such as juice, broth or commercially available products are usually recommended, but there is no recognized, effective treatment at this time. Since 1988, several drugs have been reported as treatments for cryptosporidiosis, with success varying from nonexistent to encouraging (see chart below).
Also reported frequently since 1988 has been treatment with biological agents such as chicken immunoglobulin (IGX), bovine anti-cryptosporidium immunoglobulin (BACI), bovine collostrum and bovine transfer factor. Studies of the efficacy of these products have had mixed results, ranging from disappointing to nearly complete success. Studies have been mostly with very small populations and have been difficult to design, according to Cello. Nevertheless, recently completed Phase I trials with a newly formulated high-titer bovine immunoglobulin have been very encouraging. Dr. Paul Greenberg, also involved in the initial trials, is very optimistic about the results. A new double-blind, placebo-controlled Phase II trial is currently scheduled to begin at San Francisco General Hospital. Any HIV positive individual with a diagnosis of cryptosporidiosis who would like more information may call Lisa Thurber at 415-206-4746.
Bartlett JA. Cryptosporidiosis. Project Inform Hotline Handout. Reprinted from PAAC Notes 120: 110-113. March 1993.
Cello J. UCSF/San Francisco General Hospital Department of Gastroenterology. Personal communication. December 1995.
Centers for Disease Control and Prevention. Assessing the public health threat associated with waterborne cryptosporidiosis. Workshop report. MMWR 44, #RR6. June 16, l995.
Centers for Disease Control and Prevention. Cryptosporidiosis: Fact Sheet. Document #578000. September 28, 1995.
Centers for Disease Control and Prevention. Cryptosporidiosis: A guide for persons with HIV/AIDS. Document #578001. September 25, 1995.
Ciesielski C and others. Cryptosporidiosis in AIDS patients in the United States: relationship to municipal water supplies? 2nd Conference on Human Retroviruses and Related Infections. January 29-February 2, 1995. Abstract #UI95920339.
Clavel A and others. Evaluation of the optimal number of fecal specimens in the diagnosis of cryptosporidiosis in AIDS and immunocompromised patients. European Journal of Clinical, Microbial and Infectious Diseases 14:46-49. January 1, 1995.
Coates T. San Francisco Department of Public Health Monthly Rounds. Center for AIDS Prevention Studies, San Francisco. November 30, 1995.
Cryptosporidiosis:a growing public health concern. California Morbidity. May 5, 1995.
Culotta N. National Sanitation Foundation International. Personal communication. December 1995. Current WL and others. Cryptosporidiosis. Eli Lilly and Company, Clinical Laboratory Medicine 11:873-97. December 1991.
Fenton M. Safe Drinking Water. AIDS Project of Los Angeles. 1995.
Gilson I and others. Impact of a community-wide outbreak of cryptosporidiosis on patients with AIDS. X International Conference on AIDS. August 7-10, 1994. Abstract U194371610.
Greenberg P. UCSF/San Francisco General Hospital Department of Gastroenterology. Personal communication. January 1996.
Hanna L. Cryptosporidium and other environmental pathogens. BETA. December 1994.
Hicks M. System Water Quality Superintendent, East Bay Municipal Water District. Personal Communication. October 1995.
Hsu K. Deadly parasite in water spurs scientists to improve detection. Wall Street Journal. August 8, 1995. James J. Cryptosporidium in water: CDC guidelines on how to protect yourself. Aids Treatment News 227:7-8. 1995.
Juranek D. Cryptosporidiosis: Sources of infection and guidelines for prevention. Centers for Disease Control and Prevention, Division of Parasitic Diseases. Document #578003. October 2, 1995.
Kreiger J. California Department of Health Services, Office of AIDS. Personal communication. January, 1996.
Lambert G. Cryptosporidium. The Alternative. Baltimore, MD. September 1995.
Lutz H. Preventing Cryptosporidiosis. Positive Nutrition. Autumn 1995.
McKinney K. Field Unit AIDS Surveillance Coordinator, San Francisco Department of Public Health/AIDS Office. Personal communication. January 1996.
Petersen C. Cryptosporidium and the food supply. The Lancet 345: 1128-1129. May 6, l995.
Ritchie DJ and ES Becker. Update on the management of intestinal cryptosporidiosis in AIDS. Annals of Pharmacotherapy 28: 767-78. June 1994.
Rosenberg J. California Department of Health Services/Communicable Disease Control. Personal communication, December 1995.
Sears CL. Cryptosporidiosis: epidemiology, pathogenesis and treatment. Interscience Conference on Antimicrobial Agents and Chemotherapy. October 4-7, 1994. Abstract U195921037.
United States Environmental Protection Agency, Office of Water. EPA efforts to control microbial and byproduct risk. EPA 811/F-94-005. June 1994.