Objectives: We assessed differences in HIV prevalence and sexual risk behavior among men who have sex with men (MSM) between 1997 and 2002 in San Francisco.
Methods: We used 2 population-based random-digit-dial telephone surveys of MSM households in San Francisco in 1997 (n=915) and 2002 (n=879).
Results: Estimated HIV prevalence increased from 19.6% in 1997 to 26.8% in 2002. Measures of sexual risk also increased. Unprotected anal intercourse with a partner of different or unknown HIV serostatus increased from 9.3% to 14.6%. Mean number of male partners increased from 10.7 to 13.8. The largest reported increase was 18.9% to 26.8% for "serosorting," or choosing unprotected anal intercourse partners believed to have the same HIV serostatus as oneself. Men aged 30 to 50 reported the largest increase in unprotected anal intercourse, whereas men aged 18 to 29 reported the largest increase in serosorting. Changes in the age distribution did not explain the increase in risky behavior.
Conclusions: Both HIV prevalence and sexual risk increased substantially among MSM in San Francisco between 1997 and 2002. Serosorting is being adopted more frequently than condom use by young MSM, but its effectiveness as a harm reduction strategy is not known.