Behind The Medical Headlines

Traveller's Diarrhoea

• Dr PD Welsby, Infectious Diseases Unit, Western General Hospital, Edinburgh, Scotland

Summary

To many, diarrhoea has become associated with long-haul travel and foreign holidays. It will affect up to 40% of travellers at any one time. The causes can be varied and there is often conflicting advice on prevention and treatment options. In this article, Dr Philip Welsby provides an overview of the main causes of traveller’s diarrhoea and guidance on best prevention and treatment.

Declaration of interests: No conflict of interests declared

Diarrhoea is recognised as a frequent accompaniment to foreign holidays. At any one time about 300,000 people are airborne, about 5% of journeys are to countries with significant risk of gastroenteritis, and about 40% of travellers develop diarrhoea.

In developing countries, and in some developed countries, travellers may be exposed to impure (meaning faecally contaminated) water and food, and are thus at risk of infection from a broad spectrum of pathogens. Prevention may be better than cure, but widespread use of antibiotics for prevention would be ill-advised, and advice aimed at avoiding exposure may be difficult in practice. Antibiotics can be used to prevent and treat diarrhoea, but widespread use may be counterproductive and they may also cause diarrhoea.

Treatment rests upon adequate fluid replacement, bed rest if there is much colic, exclusion from work for certain occupations, and antibiotics in selected patients.

Introduction

The main risk factor is a country of acquisition where sewage disposal may be suspect, where water supplies are not guaranteed uncontaminated, or where kitchen hygiene is not rigorously supervised. Travellers to Latin America, Africa, some of the Middle East, the Dominican Republic, Haiti, and Asia have a 20–50% incidence of diarrhoea whereas southern Europe has a risk of 8–20%.

Most travellers fall ill and recover in the country visited. With the exception of symptomatic amoebic colitis, giardiasis and tropical sprue, most infective diarrhoeas tend to be of rapid onset and rarely persist for more than two weeks. This overview deals mostly with those who have not recovered. The major causes of diarrhoea are listed in Table 1 and some relevant characteristics are detailed in Table 2.

Clinical pathophysiology of diarrhoea

The small intestine is second only to the kidney as the organ responsible for fluid balance. Small intestinal diarrhoea comprises large amounts of watery diarrhoea, which rarely contains blood, mucus, or pus. Direct invasion of the small bowel wall is one mechanism but toxins often act by stimulating production of cyclic adenine monophosphate (the ‘second messenger’) to induce the cells to secrete. This is the mechanism of cholera in which there may be a net secretion of fluid into the small bowel lumen without significant bowel wall invasion. Alternatively, malabsorptive-type small intestinal ‘porridgy’ diarrhoea can occur in giardiasis and tropical sprue. With giardia it was thought that the trophozoites lining the bowel caused malabsorption but now it is known that the syndrome can be produced by only a few organisms and that the pathology must depend on other, currently unknown, mechanisms.

Large intestinal diarrhoea is often caused by processes that invade or irritate the large intestinal wall and thus the large intestine cannot fulfil its normal function as a reservoir from which water and electrolytes are absorbed. Often, small intestinal function is unaffected by large intestinal disease, so large intestinal diarrhoea usually comprises frequent passage of small amounts of stool which may contain blood, mucus or pus. Blood in or on the stool, faecal urgency, or incontinence usually implies large intestinal problems.

Clinical features

Traveller’s diarrhoea is defined by the passage of unformed stool twice as frequently as the normal bowel habit. Most pass 4–5 stools daily. Recovery occurs within a week in 90% of cases, and <1% have symptoms at 3 months. Usually there is an abrupt onset with diarrhoea and cramps, malaise, nausea, and possibly fever. Abdominal pain is occasionally severe (see Table 2). Signs of dehydration can occur in more severe cases.

Microbiology

Shigella and amoebae are almost exclusively large bowel pathogens whereas Giardia lamblia and Vibrio cholerae are exclusively small bowel pathogens. Some pathogens, including Campylobacter jejuni and Salmonella, may produce a sequential mixed picture, with small bowel diarrhoea initially, followed by large bowel diarrhoea. Invasive pathogens often produce fever, whereas toxin-mediated illness usually does not produce a febrile response. Dysentry is diarrhoea with blood and usually implies an invasive pathogen rather than a purely toxin-mediated illness.

Bacteriological diagnosis may be suspected from symptomatology. A standard ‘stool for culture’ will not reveal non-bacterial pathogens; examination for ova, cysts, and parasites has to be requested specifically. Suspected amoebiasis is the only indication for hot stools (meaning either ‘instant microscopy’ or very rapid transport of the stool sample to the laboratory in a thermos flask). Occasionally viral examination is required. Viral examination would rarely be necessary for isolated instances of bacteriologically culture-negative diarrhoea, but may be important if there is an outbreak of bacteriologically negative diarrhoea – on cruise ships for example.

Brief duration, infection-related diarrhoeas

Staphylococcal and Bacillus cereus

These causes of food poisoning have such short incubation periods, 3–8 hours and 6–24 hours, respectively, that they are almost always acquired during the return journey. Both produce vomiting and diarrhoea of less than 24 hours duration, and are toxin-mediated.

Campylobacter

Fever and severe abdominal pain often accompany this cause of diarrhoeal illness. Occasionally abdominal pain is so severe that peritonitis or perforation is wrongly diagnosed. A significant clue to the correct diagnosis is that patients with peritonitis or perforation usually have absent bowel sounds whereas patients with invasive Campylobacter (or Salmonella) often have increased bowel sounds. Infection is usually from animal sources. Antibiotics (usually an erythromycin) are only indicated if the illness is severe or if symptoms are not improving once the diagnosis is confirmed.

Salmonella

There are three main clinical syndromes but there may be some overlap.

• The first, and most common type of illness (‘gastroenteritis’, ‘food poisoning’) is produced by infection which usually rem