The persistence of Shigella flexneri in the United States: increasing role of adult males.

The annual reported isolation rate of Shigella flexneri decreased from 1964 to 1973, but has remained constant since then at 1 per 100,000. Between 1975 and 1985, the median age of males from whom S. flexneri was isolated rose from 5 to 26 years. During this time, the isolation rate of S. flexneri rose more than five-fold among men, did not change in adult women, and decreased in children. By 1985, 23 per cent of reported S. flexneri isolates came from men aged 20-49. Increased male homosexual transmission of S. flexneri is a possible explanation for these findings.