Engagement in group sex among geosocial networking mobile application-using men who have sex with men

Background: Men who have sex with men (MSM) remain the group most affected by the HIV epidemic in the United States. At least one-quarter of MSM report engagement in group sex events (GSEs), which can pose a risk for HIV transmission and acquisition. In this study, identification of event-level correlates of sexual and drug use behaviours at GSEs was sought to better inform prevention activities. Methods: For this study, participants were recruited via banner and pop-up advertisements placed on a geosocial networking mobile phone application that MSM use to meet men. Results: Of the 1997 individuals who completed the study screener, 36.0% reported participating in at least one GSE in the prior year. In multivariable logistic regression analysis, attendance at a GSE in the past year was significantly associated with older age, full/part time employment and being HIV positive. Of the men who attended a GSE, more than half reported condomless anal sex (CAS) with at least one of their partners (insertive: 57.7%; receptive: 56.3%). MSM who indicated drug use had significantly higher odds of having insertive CAS [odds ratio (OR)≤2.45; 95% confidence interval (CI): 1.37-4.39] and receptive CAS (OR≤3.60; 95% CI: 1.96-6.63) at their last GSE. Conclusions: The high prevalence of HIV-positive MSM engaging in group sex, coupled with their greater odds of CAS, poses a significant risk for HIV/STI transmission within the group sex setting. More research is needed to determine patterns of condom use at these events and whether seroadaptive behaviours are driving CAS.