Are we systematically overestimating the risk of casual sex? New insights into accurate assessment of sexual behaviour at risk for HIV among MSM
W. Van Den Boom1, I. Stolte1, T. Sandfort2,3, U. Davidovich1
1Public Health Service Amsterdam, Cluster Infectious Diseases, Department of Research, Amsterdam, Netherlands, 2HIV Center for Clinical and Behavioral Studies, Columbia Univ, Department of Psychiatry, New York, United States, 3New York State Psychiatric Institute, New York, United States
Background: The term casual partner (CP) is usually used to encompass all types of (sex) partners that are not considered steady. A gradation exists, however, in the frequency of sex encounters and levels of familiarity with CPs. This familiarity might promote unprotected anal intercourse (UAI) but also opportunities to serosort by establishing HIV seroconcordance, and so reducing HIV transmission risk. We examined whether increased CP familiarity increases UAI, and results in more serosorting.
Methods: We surveyed 461 MSM who participate in the Amsterdam Cohort Study. Level of familiarity with a CP was determined by the frequency of sex encounters with a specific partner and by ways of contacting the CP. Three types of CP were established: one-time CP (met by chance and sex only once), multiple-time CP (met by chance on several occasions and sex on these occasions), and sex buddy (contact on regular basis for sex but not considered a steady partner). UAI at risk for HIV was defined as UAI with a CP with serodiscordant HIV status. Logistic regression analyses were used to examine the association between partner types and risk behaviour.
Results: Analyses revealed significantly more UAI with sex buddies than with one-time CPs (OR[95%CI]=2.3 [1.1-4.5]). However, due to serosorting, MSM with a sex buddy were less likely to have UAI at risk for HIV than MSM with a one-time CP (OR[95%CI]=0.19 [0.06-0.62]).
Conclusion: To accurately assess UAI, CPs should no longer be considered as one unambiguous category. Risk behaviour with a 'sex buddy' differed significantly from risk behavior with a one-time CP. Not taking the diversity of casual partner types into account results in overestimation of UAI at risk for HIV. Familiarity with a CP seems to increase the occurrence of serosorting. The protective value of serosorting with CPs needs, however, further examination.
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