TD is acquired through the consumption of contaminated food or water. Although a change in bowel habit can be caused by the stress of travel, a change in diet, and increased alcohol consumption, most episodes of TD are related to infection .

Recreational water such as swimming pools, the sea and freshwater rivers and lakes may also be a source of water-borne infection.
In swimming pools, infection may occur if treatment and disinfection of the water are inadequate. Swimming pool-related outbreaks of illness are relatively infrequent, but have been linked to viruses, bacteria, protozoa and fungi

Signs and symptoms
TD is defined as three or more unformed stools in a 24 hour period, often accompanied by at least one of the following: fever, nausea, vomiting, cramps, or bloody stools (dysentery), with symptoms usually starting during or shortly after a period of foreign travel.
Vomiting is uncommon, and dysentery (abdominal cramps with blood or mucous in the stool) is infrequent.
. TD typically occurs during the first week of arrival and is often self-limiting, lasting three to four days.

In approximately two percent of cases, symptoms persist for longer than a month . An episode of TD, particularly one with severe symptoms, can lead to irritable bowel syndrome in a small number of travellers .

Diagnosis and treatment
TD is caused by a variety of organisms. Where aetiology is known, bacteria are responsible for most cases and include ETEC, Salmonella spp., Shigella spp., and Campylobacter spp.. Enterotoxigenic Bacteroides fragilis has been identified as a likely cause of TD .
Other organisms include viruses, such as norovirus, and protozoa (e.g. Cryptosporidium spp., Giardia lamblia).

TD usually resolves spontaneously. Individuals with ongoing symptoms depending on the history and clinical presentation may require further tests, such as; stool microscopy, stool culture, full blood count and/or biochemistry.

Screening (laboratory testing) for ETEC is not usually done and up to 40 percent of TD cases never have a particular virus, bacteria, protozoa or fungi identified.

The aim of treatment of TD is to avoid dehydration, reduce the severity and duration of symptoms and reduce the interruption to travel plans .

Diet and fluid
Travellers should maintain adequate fluid intake to avoid dehydration. For a mild TD illness oral fluids are often all that is necessary.

Adults without existing health problems, with mild to moderate symptoms, can usually stay hydrated by continuing to drink and eat as normal.
Dehydration in adults is unusual, but is a concern for young children with diarrhoea. The elderly, pregnant women and those with pre-existing illness are also more susceptible to complications from dehydration .

For more severe symptoms or those prone to complications from dehydration, oral rehydration powders can be diluted into clean drinking water to remedy electrolyte (sugar/salt) imbalances. If oral rehydration powers are not available, a salt and sugar solution of six level teaspoons of sugar and one level teaspoon of salt to a litre of ‘safe’ water can be used.

Consumption of small quantities of easily digestible foods are recommended to aid gut recovery in those with TD .
Breastfeeding should be continued for infants. Children receiving semisolid foods or solid foods should continue to receive their usual diet .

Symptomatic treatment
The most common symptomatic treatments for TD are antimotility agents (e.g. loperamide), and bismuth subsalicylate.

Loperamide can be considered for travellers when frequent diarrhoea is inconvenient, e.g. those travelling on long bus journeys, or for business meetings.
However, it should not be used if the traveller has active inflammatory bowel disease (e.g. ulcerative colitis), a fever or bloody diarrhoea .
Loperamide should be used with caution; travellers should follow the instructions on the pack carefully. Loperamide preparations are available over the counter for use in adults and children over 12 years of age.
For younger children, parents should seek early medical advice if the child becomes unwell with TD and symptomatic treatment is required. Rehydration is the main treatment for TD in young children.

Bismuth subsalicylate can be recommended for mild diarrhoea and is helpful in reducing nausea. Bismuth subsalicylate preparations are available over the counter for use in adults and children over 16 years of age. However, loperamide has been shown to be more effective in controlling diarrhoea and cramping and works more quickly.

Antibiotics
Antibiotic treatment can be considered for treatment of moderate to severe travellers’ diarrhoea. A study of the use of antibiotics for acute diarrhoea in travellers and determined that there were benefits from taking antibiotics .
Those who took antibiotics had a shorter duration of diarrhoea, decreased severity of illness, and were more frequently cured within 72 hours of illness onset. Although there were more side effects in those being treated compared with those taking a placebo, these were mostly minor or resolved once the antibiotic had been discontinued.

Fluoroquinolones are often the drugs of choice when indicated . Ciprofloxacin (750mg as a single dose or 500mg twice daily for three days) is prescribed most commonly for travellers to Latin America and sub-Saharan Africa.

Fluoroquinolone resistant Campylobacter and Shigella are more common in some parts of South and Southeast Asia. For travellers to these areas azithromycin is an appropriate choice: 1,000mg single dose or 500mg once daily for three days .

Rifaximin is also licensed for the treatment of travellers’ diarrhoea that is not associated with fever, blood in the stool or eight or more unformed stools in the previous 24 hours . Clinical data have shown that rifaximin is not effective in the treatment of invasive enteric pathogens that cross the gut wall such as Campylobacter, Salmonella and Shigella which typically produce dysentery-like diarrhoea .
As travellers would have to carry a back-up drug in the event of these symptoms, the overall usefulness of rifaximin as a self treatment option remains to be determined.

The combination of loperamide with an antibiotic in moderate travellers’ diarrhoea may lead to more rapid improvement compared with either treatment alone.

Medical care
Travellers should seek medical care if symptoms do not improve within three days.
They should seek medical care immediately if they have a fever of 38oC or more, blood and/or mucous in the stool or other worrying symptoms such as altered mental status, severe abdominal pain, jaundice or rash.
Medical care should be sought earlier for the elderly, children and other vulnerable travellers if they are not tolerating fluids or are showing signs of dehydration.

G Mohan.