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We performed a randomized double-blind study to determine the efficacy of doxycycline (100 mg daily) in preventing travelers' diarrhea among 39 Peace Corps volunteers during their first five weeks in Kenya. The volunteers took either doxycycline or placebo for three weeks and were observed for an additional two weeks. Nine of 21 taking placebo and one of 18 taking doxycycline had travelers' diarrhea during the treatment period (P = 0.012). The protection seemed to persist for at least one week after the drug was stopped. Enterotoxigenic Escherichia coli was the only pathogen isolated from the placebo group, but was not detected in persons taking doxycycline. None of these organisms were resistant to doxycycline or tetracycline, whereas resistance to tetracyclines and other antibiotics was common among the nonenterotoxigenic Esch. coli. We conclude that doxycycline effectively prevented most episodes of travelers' dirrhea.

Travelers' diarrhea was studied prospectively in a group of 39 American Peace Corps Volunteers (PCVs) during their first five weeks in Kenya. Twenty-seven developed diarrheal disease and 12 remained well. Multiple episodes were documented in 11 of the symptomatic volunteers. Enterotoxigenic Escherichia coli of many serotypes producing heat-labile and/or heat-stable enterotoxin were isolated from 17 of the 27 volunteers with diarrhea and from 1 of the 12 well volunteers. The enterotoxigenic E. coli were more likely to be antibiotic sensitive than the non-enterotoxigenic E. coli. A serum antibody rise to the heat-labile toxin (LT) was detected in six symptomatic volunteers, five of whom had a positive culture for LT-producing E. coli, and from one asymptomatic, culture negative volunteer. Salmonella cubana was isolated from two volunteers, and three volunteers had serologic evidence of infection with human reovirus-like (rotavirus) agent. This study confirms the role of enterotoxigenic E. coli as a major cause of travelers' diarrhea and suggests that the disease is similar in widely separated geographic areas.