Prevention of Travelers' Diarrhea With Trimethoprim-Sulfamethoxazole and Trimethoprim Alone

One hundred forty-five students from the United States enrolled in a study designed to look at the protective effect of trimethoprim-sulfamethoxazole or trimethoprim alone in preventing diarrhea during study in Mexico. A highly significant difference (p Escherichia coli was isolated from a diarrheal stool of 3 of 8 students receiving trimethoprim alone and from stool of 5 of 10 students with illness who were taking a placebo. A Shigella strain was detected in specimens from 3 of 10 students and a Salmonella strain was identified in the stool of one student in the group receiving the inactive placebo. Neither Shigella nor Salmonella were identified in students taking either active preparation. One enterotoxigenic E. coli strain (an ST-only) in a trimethoprim-treated student with diarrhea was found to be resistant to trimethoprim-sulfamethoxazole and to trimethoprim. The remaining enteropathogens identified with diarrhea either during the 14-d trial or the 1-wk posttreatment, including 14 enterotoxigenic E. coli strains, 12 Shigella strains, and 2 Salmonella strains, were each susceptible to trimethoprim-sulfamethoxazole. In the present study, trimethoprimsul famethoxazole and, to a lesser extent, trimethoprim alone, was effective in preventing traveler's diarrhea for a period of 2 wk when taken once a day. Infection by enterotoxigenic E. coli and Shigella strains was prevented and illness commonly occurred once the drugs were stopped and the students remained in Mexico, underscoring the need for continuing the drugs as long as the traveler is at risk.