Referring to the 2010 report “Foreign travel-associated illness: a focus on travellers’ diarrhoea” by the then Health Protection Agency, the TravelHealthPro (THP) website asserts the statement that
“Travellers’ diarrhoea (TD) is the most common health problem of overseas travellers, affecting an estimated 20 to 60 percent of those who travel to high risk destinations of the world.”Factors which determine how likely an individual is to get TD include
- Age – the most important host factor, with children and teenagers constituting the highest risk group for TD , although it can affect a person at any age
- Destination – see below
- Diet and choice of eating establishment – street food vendors may be more visible in their neglect of food preparation hygiene standards, but any establishment in endemic disease areas where there is a high level of hand contact with food by third parties is a potential risk 
- Duration of travel – overseas stays of more than one week are considered a risk factor , but that’s not to say you can’t contract TD as soon as you arrive overseas
- Host genetics – some people have a genetic profile that can contribute to greater risk
- Season of travel – in some destinations seasonal climatic changes may affect the chances of getting TD, while in other locations such variations seem to make little difference
- Sourcing of drinking water – the selection of drinking water is a significant factor in the risk of acquiring TD. If you can’t find an answer to a question about drinking water safety on this website please get in contact.
- Type of travel – unsurprisingly, budget backpacking is generally considered to be a greater risk than luxury vacation travel, although the latter is no guarantee of avoiding TD, and in some circumstances may actually increase the risk. Remote locations visited by such as climbers and trekkers may increase infection incidence 
Gender is not normally regarded as a determining factor; your sex won’t save you or make you more likely to contract TD Pre-existing health conditions don’t usually increase susceptibility to TD,although “diarrheal episodes in the 2 months pre-travel period and the use of antacids significantly increased the risk of TD”.
Of all these factors, we consider the destination country and the choices made with regard to food and water to be the most important in determining the risk of contracting TD.
As is indicated by the term “high risk destinations” in the initial quotation, not all places are equal when it comes to travellers’ diarrhoea. Whilst in reality the likelihood of infection may vary significantly within a country, destinations have been broadly nationally classified as being either “low”, “intermediate” or “high” in terms of the risk of contracting TD.
Low risk is defined by the UK HPA and others as 7% or less chance of contracting TD, intermediate risk as 8% to 20%, and high risk as >20% to 60%. The US CDC states that “attack rates range from 30% to 70% of travellers” but also uses a low/intermediate/high grading system for countries.
Diagram 1: Map of TD relative risk areas.
Despite identifying destinations in terms of relative risk,
in the UK reporting and laboratory confirmation of TD incidence “represents the tip of the iceberg in relation to the estimated number of illnesses that actually occur in travellers.”
Using UK Office for National Statistics (ONS) figures for 2015 and 2016 (see Table 3 at the end of this post) it is possible to identify an annual breakdown of overseas travel by UK residents by country (or regional group), which in turn enables a more accurate breakdown of TD risk.
Table 1: UK travel to named overseas destinations by area of risk and potential incidence of Traveller’s Diarrhoea, 2015 and 2016:
These figures are, of course, statistical possibilities, but if they only serve to give an indication of the scale of the TD potentially being experienced by UK travellers, it is obvious that a significant healthcare issue is routinely and repeatedly being neglected.
In 2015 a figure of approximately 8.7 million cases would have meant that 13.37% of the total number of over 65 million travellers had been affected by TD. This figure was marginally reduced to 13.13% for 2016, but this is likely to reflect choices that rejected ‘high risk’ countries in favour of ‘low’ and ‘intermediate’ risk destinations on the basis of parallel political evaluation rather than gastrointestinal considerations. Overall traveller numbers continued to rise in 2016, and, predicted to continue doing so in coming years, there is no reason to think that the incidence of TD will be falling without a considerable change in attitudes to this affliction.
The risk for US citizens is even more alarming. When we first put this page together we only had figures for 2015, at which time the U.S. Department of Commerce’s National Travel and Tourism Office listed the 43 most popular overseas destinations for US outbound travellers. This figure was reduced to 38 countries when the 2016 figures became available (see summary in Table 4 at the end of this post), which highlights that this is an incomplete, if strongly indicative, calculation of total TD occurrence. The total number of US residents’ trips in 2016 was 80.2 million. For reasons of comparative conformity we once again applied HPA median definitions of risk, and the results can be seen in the updated Table 2 below.
Table 2: US travel to named overseas destinations by area of risk and potential incidence of Traveller’s Diarrhoea, 2015 to 2016:
What is immediately noticeable about these figures is not only the increasing number of trips being made overseas, but the large number of Americans travelling to high risk destinations. This is predominantly due to the fact that nearly 29 million US citizens travelled to Mexico in 2015, a figure which rose to over 31 million in 2016.
What is perhaps more surprising is why a little under 1 in 4 of over 78 million travellers would potentially deem a dose of Montezuma’s Revenge (or other local equivalents) to be an acceptable level of illness simply because they’ve headed overseas.
It may be that in the face of overwhelming levels of infection we simply regard TD as an unavoidable fact that comes with the territory if we are to undertake international travel, and one that is best dealt with by stoic endurance of an illness that is mostly self-limiting, and generally just a bit of a pain in the proverbial. However, if you’d like to know about the more serious effects and potential cost of TD take a look at this news post.
If you’d like to reduce the risk of contracting travellers’ diarrhoea
• Contact your travel health provider today and ask them for advice on the TD risk at your next destination
• Read more in the Water Matters and other sections of this website
References [click on the reference number to access the source documentation online].
 Health Protection Agency; Foreign travel-associated illness: a focus on travellers’ diarrhoea (2010)
 “TravelHealthPro is the website comprising the travel health resources of the National Travel Health Network and Centre (NaTHNaC).” It contains a Travellers’ Diarrhoea Factsheet page.
 Robert Steffen, MD; Epidemiology of travellers’ diarrhea. J Travel Med 2017; 24 (suppl_1): S2-S5
 Steffen, R., Tornieporth, N., Costa Clemens, S.-A., Chatterjee, S., Cavalcanti, A.-M., Collard, F., De Clercq, N., DuPont, H. L. and von Sonnenburg, F. (2004); Epidemiology of Travelers— Diarrhea: Details of a Global Survey. Journal of Travel Medicine, 11: 231–238
 Bradley A. Connor; Travellers’ diarrhea. CDC Yellow Book online.
 US Dept. of Commerce “U.S. Resident Travel to International Destinations Increased Eight Percent in 2016″, December 2016
Table 3: UK Residents Visits Abroad 2015 and 2016 by TD risk area.
Table 4: US Residents Visits Abroad 2015 and 2016 by TD risk area.