Background:  Seroadaptation refers to a wide range of harm reduction practices based on the knowledge of one’s own serostatus and that of one’s sexual partners in order to decrease risk of HIV acquisition and transmission. However, use of the term to describe the pattern of sexual behavior for individuals belies the fact that behavior may vary with different partners. The present study extends the framework to compare the prevalence of seroadaptive behaviors across 3 perspectives:  the individual, the sexual dyad, and the sexual episode.

Methods:  Men who have sex with men (MSM) were recruited from December 2007 to October 2008 using time-location sampling methodology. Recruitment took place at venues in San Francisco where the clientele were primarily MSM. Seroadaptive behaviors in the preceding 6 months were evaluated among individuals (n = 1207 persons), within sexual dyads (n = 3746 partnerships), and by sexual episodes (n = 63,789 episodes). Mutually exclusive hierarchical categories of sexual behaviors were created based upon previous definitions and relative HIV transmission probabilities.

Results:  Seroadaptation of some form was practiced consistently by 39.1% of MSM at the individual level and was a more common risk-reduction strategy than 100% condom use (25.0%), no oral or anal sex (13.6%), and oral sex only (12.3%). Pure serosorting, defined as unprotected anal intercourse with seroconcordant partners, was practiced by 22.3% of MSM. At the sexual dyad level, 100% condom use was more common than seroadaptation (33.1% vs 26.4%). At the sexual episode level, oral sex (65.0%) and anal intercourse using condoms (16.0%) were the most common risk-reduction behaviors. Seroadaptation occurred in 17.4% of sexual episodes, primarily unprotected anal intercourse with HIV seroconcordant partners (14.6%) or in the context of seropositioning (2.8%). Unprotected anal intercourse with an HIV serodiscordant or unknown status partner in the riskier position occurred in only 1.6% of sexual episodes.

Conclusions:  MSM engage in risk-reduction behavior the vast majority of the time and achieve a high level of sexual harm reduction through multiple strategies. Seroadaptation plays a major role in risk reduction, but not as the predominant strategy or in isolation of other strategies. Detailed measures of seroadaptive behaviors are needed to effectively target HIV risk and gauge the potential impact of serosorting and related sexual harm reduction strategies on the HIV epidemic.