The San Francisco Men's Health Study: continued decline in HIV seroconversion rates among homosexual/bisexual men.

The incidence of infection by the human immunodeficiency virus (HIV) has been monitored since 1984 in an area probability sample of homosexual/bisexual men drawn from a six-kilometer square area of San Francisco where the epidemic of acquired immunodeficiency syndrome (AIDS) has been most severe. Annualized HIV seroconversion rates in previously uninfected cohort members have declined by 88 per cent from 5.9 per cent during the first six months of 1985 to 0.7 per cent during the last six months of 1987. Concurrent declines of approximately 80 per cent in the prevalence of sexual behaviors associated with HIV transmission were also observed in the sample.