Chapter 117. Health Advice for International Travel (Part 4) Prevention of Gastrointestinal Illness Diarrhea, the leading cause of illness in travelers (Chap. 122), is usually a short-lived, self-limited condition; however, 40% of affected individuals need to alter their scheduled activities, and another 20% are confined to bed. The most important determinant of risk is the destination. Incidence rates per 2-week stay have been reported to be as low as 8% in industrialized countries and as high as 55% in parts of Africa, Central and South America, and Southeast Asia. Infants and young adults are at particularly high risk. A recent review suggested that there is little correlation between dietary indiscretions and the occurrence of travelers' diarrhea. Earlier studies of U.S. students in Mexico showed that eating meals in restaurants and cafeterias or consuming food from street vendors was associated with increased risk. Etiology (See also Table 122-3) The most frequently identified pathogens causing travelers' diarrhea are toxigenic Escherichia coli and enteroaggregative E. coli (Chap. 143), although in some parts of the world (notably northern Africa and Southeast Asia) Campylobacter infections (Chap. 148) appear to predominate. Other common causative organisms include Salmonella (Chap. 146), Shigella (Chap. 147), rotavirus (Chap. 183), and norovirus (Chap. 183). The latter virus has caused numerous outbreaks on cruise ships. Except for giardiasis (Chap. 208), parasitic infections are uncommon causes of travelers' diarrhea. A growing problem for travelers is the development of antibiotic resistance among many bacterial pathogens. Examples include strains of Campylobacter resistant to quinolones and strains of E. coli, Shigella, and Salmonella resistant to trimethoprim-sulfamethoxazole. Precautions Although the mainstay of prevention of travelers' diarrhea involves food and water precautions, the literature has repeatedly documented dietary indiscretions by 98% of travelers within the first 72 h after arrival at their destination. The maxim "Boil it, cook it, peel it, or forget it!" is easy to remember but apparently difficult to follow. General food and water precautions include eating foods piping hot; avoiding foods that are raw, poorly cooked, or sold by street vendors; and drinking only boiled or commercially bottled beverages, particularly those that are carbonated. Heating kills diarrhea-causing organisms, whereas freezing does not; therefore, ice cubes made from unpurified water should be avoided. Self-Treatment (See also Table 122-5) As travelers' diarrhea often occurs despite rigorous food and water precautions, travelers should carry medications for self-treatment. An antibiotic is useful in reducing the frequency of bowel movements and duration of illness in moderate to severe diarrhea. The standard regimen is a 3-day course of a quinolone taken twice daily (or, in the case of some newer formulations, once daily). However, studies have shown that a single double dose of a quinolone may be equally effective. For diarrhea acquired in areas such as Thailand, where >90% of Campylobacter infections are quinolone resistant, azithromycin may be a better alternative. Rifaximin, a poorly absorbed rifampin derivative, is highly effective against noninvasive bacterial pathogens such as toxigenic and enteroaggregative E. coli. The current approach to self-treatment of travelers' diarrhea is for the traveler to carry three once-daily doses of an antibiotic and to use as many doses as necessary to resolve the illness. If neither high fever nor blood in the stool accompanies the diarrhea, loperamide may be taken in combination with the antibiotic. Prophylaxis Prophylaxis of travelers' diarrhea with bismuth subsalicylate is widely used but only ~60% effective. For certain individuals (e.g., athletes, persons with a repeated history of travelers' diarrhea, and persons with chronic diseases), a single daily dose of a quinolone or azithromycin or a once-daily rifaximin regimen during travel of <1 month's duration is 75–90% efficacious in preventing travelers' diarrhea. Illness after Return Although extremely common, acute travelers' diarrhea is usually self- limited or amenable to antibiotic therapy. Persistent bowel problems after the traveler returns home have a less well-defined etiology and may require medical attention from a specialist. Infectious agents (e.g., Giardia lamblia, Cyclospora cayetanensis, Entamoeba histolytica) appear to be responsible for only a small proportion of cases with persistent bowel symptoms. By far the most frequent causes of persistent diarrhea after travel are postinfectious sequelae such as lactose intolerance or irritable bowel syndrome. A recent meta-analysis showed that postinfectious irritable bowel syndrome may occur in as many as 4–13% of cases. When no infectious etiology can be identified, a trial of metronidazole therapy for presumed giardiasis, a strict lactose-free diet for 1 week, or a several-week trial of high-dose hydrophilic mucilloid (plus lactulose for persons with constipation) relieves the symptoms of many patients. . Chapter 117. Health Advice for International Travel (Part 4) Prevention of Gastrointestinal Illness Diarrhea, the leading cause of illness in travelers (Chap. 122),. outbreaks on cruise ships. Except for giardiasis (Chap. 208), parasitic infections are uncommon causes of travelers' diarrhea. A growing problem for travelers is the development of antibiotic. therefore, ice cubes made from unpurified water should be avoided. Self-Treatment (See also Table 122-5) As travelers' diarrhea often occurs despite rigorous food and water precautions, travelers