Knowledge of sexual partner's HIV serostatus and serosorting practices in a California population-based sample of men who have sex with men.

OBJECTIVES: To describe knowledge of primary and secondary sexual partner's HIV serostatus and sexual practices, including serosorting, among men who have sex with men (MSM) living in California.

METHODS: Men who self-identified as gay/bisexual in the 2001 California Health Interview Survey, a statewide biennial random-digit-dial survey interviewing more than 50,000 adults on a variety of health topics, were recontacted in 2002 and interviewed by telephone about injection drug use, their own and partner's HIV serostatus, and sexual risk behaviors.

RESULTS: Among 220 men who reported a primary partner, 86% [95% confidence interval (CI): 77-92] knew their primary partner's serostatus; 62% (95% CI, 52-70) of the 250 men who reported a secondary partner knew their most recent secondary partner's HIV serostatus. Knowledge of one's most recent secondary partner's HIV serostatus was inversely related to history of injecting recreational drugs (odds ratio, 0.22; P < 0.01), and reporting a primary partner in the past year (odds ratio, 0.37; P < 0.05). Two-fifths (41%) of HIV-positive men and three-fifths (62%) of HIV-negative men engaged in serosorting (serocordant unprotected anal intercourse) with their primary partners, whereas 33% HIV-positive men and 20% HIV-negative men did so with their most recent secondary partners.

CONCLUSIONS: This population-based survey documented the extent to which MSM know their partners' serostatus and practice serosorting behaviors. The findings emphasize the need for studies to report serocordant and serodiscordant unprotected anal intercourse separately, as the former presents significant lower risk of HIV transmission.