P1-S2.47 Serosorting and sexual risk behaviour during casual sex among MSM - from one-night stands to sex buddies

Background Among HIV-negative men who have sex with men (MSM), any incident of unprotected anal intercourse (UAI) between casual partners is usually regarded as risky for HIV. However, men are increasingly using knowledge of their casual partner's HIV-status to reduce the risk for HIV during UAI (serosorting). Since familiarity between casual partners may lead to higher levels of UAI and serosorting, we examined how often men have UAI and report serosorting with three casual partner types that differ in the degree of familiarity. Methods We included 240 HIV-negative men of the Amsterdam Cohort Study among MSM. We distinguished three casual partner types—one-night stand (“met by chance and had sex only once”); multiple-time casual partner (“met by chance and had sex several times”); and sex buddy (“contacted on a regular basis for sex but not considered a steady partner”). Serosorting was defined as UAI with an HIV-negative partner. GEE analyses were performed to examine the association between casual partner type and sexual risk behaviour. Results 240 participants accounted for 362 reports of anal intercourse, of which 206 (57%) with one-night stands, 95 (26%) with multiple-time casual partners, and 61 (17%) with sex buddies. The proportion of UAI was 19% (39/206) with one-night stands, 20% (19/95) with multiple-time casual partners, and 34% (21/61) with sex buddies. When performing UAI, 21% (8/39) reported serosorting with one-night stands, 42% (8/19) with multiple-time casual partners, and 52% (11/21) with sex buddies. Analyses revealed that only men with a sex buddy were significantly more likely to have UAI (OR [95% CI] 2.39 [1.39 to 4.09]), but were also more likely to practice serosorting than men with a one-night stand (OR [95% CI] 5.20 [1.20 to 22.52]). No differences were found between the multiple-time casual partner and the other partner types. Conclusions Men with a sex buddy had more UAI but also reported more serosorting than men with a one-night stand. As a result, the proportion of UAI without serosorting is lower for men with a sex buddy, and therefore men might have less UAI at risk for HIV with this partner type. However, the quality of serosorting with casual partners and hence their protective value against HIV needs to be further established. At this time, we suggest that a distinction between the one-night stand and the sex buddy should be incorporated in future studies as risk behaviour of MSM is significantly different between thes