Data for MSM continue to show a high risk of acquiring HIV-STIs. Within this population, outness seems to have an impact on both risk-taking and on health seeking behaviors. The objective of this study was to assess the relationship between socio-demographic, behavioral characteristics, testing behaviors, and outness level among MSM using data from a multi-center bio-behavioral cross-sectional study carried out in 13 EU cities. A multilevel analysis was conducted to identify factors associated with being open ("out") versus not being open ("in"). A total of 4,901 MSM were enrolled in the study and were classified as "out" in 71% of the cases. MSM "out" were more likely to report HIV testing and being reached by HIV prevention programs compared to MSM who were "in." The results confirm the key role of outness in relation to different healthy and risky behavior, ranging from testing to party-drug use.
Keywords: HIV testing; MSM; Time-Location Sampling; bio-behavioral survey; outness; respondent-driven sampling; risk behaviors.