Key learning points:
- A substantial number of travellers are at risk of food and water-borne infections due to the increase in travel to these areas - Optimising the management of symptoms and treatment should replace advice on avoidance and risk behaviour
There were an estimated 460 million international travellers globally in 2011 to areas where poor standards of hygiene and sanitation exist,1 placing a substantial number of travellers at risk of food and water-borne infection. Traveller’s diarrhoea (TD) remains the most common ailment, affecting 40% to 50% of travellers.1 Other food and water-borne illnesses which travellers may acquire include hepatitis A, enteric fever (typhoid and paratyphoid) and, very rarely, cholera.
This article focuses on traveller’s diarrhoea, aetiology, how to identify those at risk and how to approach its prevention and management.
Symptoms and sequelae of travellers’ diarrhoea
Travellers’ diarrhoea is when an individual has three or more unformed stools in 24 hours, often accompanied by symptoms such as abdominal pain or cramps, faecal urgency, nausea and vomiting.
For most young healthy travellers it is self-limiting, lasting approximately 3-5 days, and rarely gives rise to serious illness. However, around 20% of those affected can have up to 20 stools a day2 and around a third are unable to pursue planned activities,3 which has an important impact on those taking short holidays. Between 3% and 10% of individuals with TD will go on to develop signs of invasive infection with fever and/or bloody/mucoid stools, but fortunately few (less than 1%) will require hospitalisation.4 TD has been implicated in triggering inflammatory bowel disease and an estimated 10% of those who have had TD develop irritable bowel syndrome.3
Pathogens responsible for traveller’s diarrhoea
Bacteria and their toxins are responsible for most cases of TD (50% of symptomatic TD episodes2). The commonest bacterial infection associated with TD is Escherichia coli, estimated to cause up to two thirds of epsiodes, and Enterotoxigenic E coli (ETEC) is the most important. Other bacterial agents include Campylobacter spp., Salmonella spp., Shigella spp., Aeromonas spp., Pleisiomonas, and non cholera vibrios, while Vibrio cholerae is rarely identified.
Viruses account for a minority of illnesses; however, norovirus (a highly infectious agent) is often associated with acute diarrhoea and vomiting outbreaks on cruise ships. Rotavirus is infrequently associated with acute TD.
Parasitic causes of diarrhoea include Entamoeba histolytica, Giardia lamblia, and Cryptosporidium parvum. Giardia is a cause of prolonged diarrhoea in travellers visiting India and Egypt5, but is now a rare cause of TD, while amoebiasis (an infection caused by the protozoan parasite, E.Histolytica), leading to bloody diarrhoea, is a rare problem in travellers.
Other food and water-borne infections
Hepatitis A is a viral infection common in areas of the world where sanitation is poor. A high proportion of infections are asymptomatic, particularly in young children, but it may be severe and prolonged in adults, and for this reason prevention through vaccination is recommended for most travel to developing countries.
The risk of typhoid and paratyphoid, caused by Salmonella Typhi and Paratyphi A, B or C is greatest for travellers to the Indian subcontinent, over 90% of imported infections in the UK come from this region.6
Cholera (Vibrio cholerae) infection is extremely rare in travellers and vaccination is usually only warranted for those with prolonged stays in outbreak situations, such as humanitarian aid workers.
Seafood poisoning from marine toxins is associated with the ingestion of reef fish. Symptoms are predominantly paraesthesia and loss of sensation of cold and hot objects, and occasionally non-specific neuropsychiatric symptoms hours after eating contaminated fish. These may persist for many weeks.
Risk factors and risk groups
A pre-travel risk assessment will help identify and reduce the risk to those most susceptible to TD and its complications. Host factors (such as age, behaviour and nationality) and environmental factors (such as destination, accommodation and length of stay) play an important role in risk. Table 1 lists information that should be sought pre-travel to help identify those most at risk.
Management of travellers’ diarrhoea
Travellers need to be made aware of how to manage a bout of diarrhoea, and when to seek medical help. This advice is particularly important for parents of young children, older travellers with underlying diseases who are at increased risk of becoming dehydrated, and those for who diarrhoea may give rise to more severe illness.
Oral rehydration therapy (ORT) is usually unnecessary for healthy adults who can replace fluid and salt loss through normal food and fluid but is important for infants, young children, older travellers and those with pre-existing medical conditions.
Prevention of traveller’s diarrhoea
The prevention of TD has traditionally focused on advice about food and water hygiene, and although travellers should be reminded about common-sense measures in choosing, preparing and handling food, there is no evidence that this type of advice has had any impact on reducing the incidence of TD or that travellers adhere to the advice. In recent years there has been a change to either preventing TD through the use of chemoprophylactic measures (antimicrobial/antibacterial drugs) or, as more widely practised, treating the symptoms of TD rapidly as they occur.
Anti-motility agents such as Loperamide provide effective relief for mild to moderate diarrhoea but it does not treat the underlying cause and so relapse of symptoms can occur.7 They should not be used in young children, or in adults with bloody diarrhoea.2
Chemoprophylaxis with antibiotics such as the fluorquinolones (eg.ciprofloxacin), doxycycline and trimethoprim/sulfamethoxazole have been shown to be effective in reducing the incidence of TD by between 58% and 100%,8 but their use needs to be balanced with the risk of adverse events, drug resistance and Clostridium difficile-associated diarrhoea. The groups most likely to benefit from chemoprophylaxis are those who need to travel short-term for important events (for example athletes and politicians) and those with underlying medical problems, particularly those with gastrointestinal pathology.
A more recent approach to the prevention of TD has been the development of vaccines to protect against a limited number of bacterial pathogens, particularly Escherichia coli (ETEC).
The oral cholera vaccine (Vibrio cholerae whole cell/recombinant B subunit vaccine) has been shown to provide some benefit against cholera, and in some countries it is licensed for the prevention of TD. However it is reported to have limited protective efficacy in travellers, preventing ≤ 7% cases of TD,2 and is not licensed for this use. Cholera is a very uncommon cause of TD and its use is limited to individuals working in outbreak situations.
Vaccines to protect against Shigella, Campylobacter, ETEC and Norovirus infections are undergoing human trials. However, vaccines will only be successful as a preventive strategy if they are able to protect against a range of pathogens responsible for TD.
Self-treatment of traveller’s diarrhoea
Rather than using chemoprophylaxis, many travel medicine experts feel it appropriate to provide travellers to high-risk areas medication for self-therapy to reduce the symptoms and duration of diarrhoea.9 The fluoroquinololes such as ciprofloxacin are most widely used and a single dose of 500 mg is effective if taken early. Where quinolone resistance is widespread, as in South East Asia and the Indian subcontinent, Azithromycin or Rifaximin can be used. Rifaximin is newly licensed for the treatment of uncomplicated non-invasive TD in adults. It remains in the gastrointestinal tract with little systemic absorption and potentially fewer adverse events than an absorbed drug.9
The rapid growth in overseas travel, particularly to developing countries, puts large numbers of travellers at risk of food and water-borne infections. Strategies to prevent infection have focused on education and motivating travellers to exercise care in food and beverage selection. These interventions have had limited impact and in recent years there has been a shift towards the use of rapid self-treatment of traveller’s diarrhoea. Vaccines that protect against a wide range of TD-causing pathogens are needed but are unlikely to be available in the near future.
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8. DuPont HL, Ericsson CD, Farthing MJ, Gorbach S, Pickering LK, Rombo L et al. Expert review of the evidence base for prevention of travelers’ diarrhea. J Trav Med 2009;16(3):149-160.
9. DuPont HL, Ericsson CD, Farthing MJ, Gorbach S, Pickering LK, Rombo L et al. Expert review of the evidence base for self-therapy of travelers’ diarrhea. J Trav Med 2009;16(3):161-171.
10. Craig R, Mindell J. Health Survey for England 2005. The health of older people. The National Centre for Social Research. Rachel Craig, Jennifer Mindell (Eds) 1-21. 2007. The Information Centre.
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