Abstract
BACKGROUND: Specific high-risk subgroups of men who have sex with men (MSM) play crucial roles in sexually transmitted infection (STI) transmission. This study investigated temporal trends in sexual behaviors and associated factors among bisexual MSM, active MSM, and active MSM in bisexuality. METHODS: From 2010 to 2023, MSM were recruited in Zhejiang, China, through multiple strategies, including community popular opinion leader (CPOL) outreach, venue-based sampling (VBS), HIV voluntary counseling and testing (VCT) clinics, and online platforms. MSM who reported anal sex in the past six months and completed a standardized survey were classified into three high-risk subgroups. We used chi-square trend tests and weighted multivariable logistic regression analyses to assess temporal trends and associated factors. Additionally, SHapley Additive exPlanations (SHAPs) were applied to evaluate the relative importance of predictors. RESULTS: Among the 4197 MSM, 2709 were classified as high-risk, with the proportions of the three high-risk subgroups showing gradual declines but remaining above 20%. Significantly, the rate of consistent condom use has decreased since COVID-19. Weighted logistic regression revealed that bisexual MSM were less likely to be recruited from networks (OR 0.70, 95% CI: 0.21–0.89), younger (OR 0.97, 95% CI: 0.96–0.98), and married (OR 12.68, 95% CI: 10.38–15.33). Active MSM were more likely to be recruited from public bathhouses/sauna rooms/foot spas/massage spas (OR 1.58, 95% CI: 1.32–1.88), had lower education (OR 0.70, 95% CI: 0.61–0.82), and reported lower consistent condom use (OR 0.73, 95% CI: 0.63–0.86). Engagement in commercial anal sex was associated with all three high-risk subgroups (bisexual MSM: OR 2.86, 95% CI: 2.10–3.86; active MSM: OR 1.84, 95% CI: 1.39–2.43; active MSM in bisexuality: OR 2.18, 95% CI: 1.40–3.39). CONCLUSIONS: Despite gradual declines, the proportions of high-risk MSM remain substantial, and the decline in consistent condom use since COVID-19 underscores ongoing prevention challenges. Married MSM, younger bisexual MSM, active MSM with lower education, those recruited from public venues, and individuals engaging in commercial sex represent key targets for future targeted interventions to reduce STI transmission. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12889-025-25517-8.