Types of Group Sex and Their Association with Different Sexual Risk Behaviors Among HIV-Negative Men Who Have Sex with Men.

The current study sought to identify types of group sex acts among HIV-negative men who have sex with men (MSM) and assess their association with different sexual risk behaviors using cross-sectional data of group sex acts reported during 6 waves (2015-2018) of the Amsterdam MSM Cohort Study. Latent class analysis was performed to identify group sex types based on size, familiarity with partners, location, planning, and drug use. Associations between group sex types and sexual behaviors were evaluated using logistic regression with generalized estimating equations, employing the sample mean as a reference. Data at the level of group sex acts were analyzed, while correcting variance estimations for repeated measurements within MSM. A total of 392 MSM engaged in group sex ≥ 1 times, totaling 1033 group sex acts. Four types of group sex emerged: familiar (29%), intimate (27%), impromptu (36%), and party (8%). Familiar group sex (characterized by high proportions of mostly known partners, occurring in private places and involving drug use) had an increased adjusted odds of risky fingering (aOR 1.6, 95%CI 1.3-2.0) and of risky fisting and/or use of sex toys (aOR 2.3, 95%CI 1.6-3.1). Intimate group sex (characterized by high proportions of threesomes, occurring in private places, and not involving drug use) had a decreased adjusted odds of risky fisting and/or use of sex toys (aOR 0.6, 95%CI 0.4-0.9). Impromptu group sex (characterized by high proportions of spontaneity, mostly unknown partners, and taking place in public places) had a decreased adjusted odds of risky fisting and/or use of sex toys (aOR 0.5, 95%CI 0.3-0.7) and of condomless anal intercourse (CAI) (OR 0.6, 95%CI 0.5-0.8). Party group sex (characterized by high proportions of larger groups, mostly unknown partners, and being planned) had an increased adjusted odds of risky fisting and/or use of sex toys (aOR 1.6, 95%CI 1.0-2.7) and of CAI (aOR 1.5, 95%CI 1.1-2.1). The identified types of group sex reflect different dynamics and characteristics, with some types riskier for STIs and others riskier for HIV. HIV and STI prevention efforts could be tailored accordingly. For example, in certain type of public sex environments (e.g., cruising parks), traditional HIV and STI prevention efforts, such as promoting of condom use and PrEP, might be sufficient. However, in other settings (e.g., private parties), where group sex is more likely to be planned and where behaviors such as fisting, sharing of sex toys, and CAI are more likely to take place, which carry different levels of risk for HIV and STI transmission, including that of Hepatitis C, different approaches might be needed, such as broader HIV and STI prevention education efforts or targeting the organizers of group sex events.