Factors associated with human immunodeficiency virus seroconversion in homosexual men in three San Francisco cohort studies, 1984-1989.

A total of 83 HIV seroconversions occurred between 1984 and 1989 in three San Francisco cohorts of homosexual and bisexual men. A nested case-control analysis was performed to assess the risk of seroconversion associated with sexual practices. Strong associations were found with total number of intercourse partners and receptive anal intercourse. Weaker, but significant associations were found with receptive oral intercourse. Individuals reporting condom use with some partners were more likely to become infected than those reporting no condom use. Some of this difference was due to increased numbers of sexual partners among those reporting some condom use, but the association remained significant in multivariate analyses. This observation indicates there is some unmeasured risk associated with those using condoms, such as more HIV seropositive partners.