Doxycycline prophylaxis for shigellosis.

The efficacy of oral doxycycline, 100 mg/d for 14 days, in reducing the incidence of shigellosis in newcomers to an area hyperendemic for the disease was examined in a double-blind, placebo-controlled trial. Of 107 entrants, 100 completed the study; 50 received the drug and 50 received a placebo. Diarrheal disease and associated symptoms were monitored for 8 weeks. Starting on the 3rd day of the trial, an outbreak was observed, and Shigella flexneri type 2a was isolated from 6 subjects. Eight of the subjects in the treatment group had diarrhea (16%) compared with 37 in the placebo group (74%), providing a 79% protection rate. There was no significant difference in the occurrence of accompanying symptoms between the subjects suffering from diarrhea in both groups, but the duration of disease was shorter in the treatment group. Serologic study of the outbreak showed no significant difference in antibody response to S flexneri between the treatment (14 of 43) and placebo (18 of 39) groups. Doxycycline prophylaxis apparently is effective and probably does not prevent subclinical infection.