Partnership-based sexual behaviours among adults in Singapore

Introduction Sexual behaviour data are essential for monitoring behavioural trends and designing effective sexual health interventions. However, in Singapore and Southeast Asia more broadly, most research has focused on key populations, leaving a decades-long research gap in the general adult population. To address this, characterised sexual behaviour patterns and examined associations with socio-demographic characteristics, engagement with sex workers, and STI positivity. Methods We conducted a nationwide cross-sectional online survey (September 2023 to July 2024). Of 2,876 respondents, 2,297 were eligible (aged 21 years and above with complete key demographic data). Participants reported socio-demographic characteristics and sexual behaviours within the past year, 6 months, and 3 months. Outcomes included fitted distributions of partner numbers across partnered activities (mutual masturbation, oral, vaginal, anal sex) and associations with socio-demographic factors, sex worker engagement, and self-reported STI positivity. Results Of participants, 51.5% were male, 84.4% were Singapore citizens, 69.6% were aged between 21-60. Individuals reporting sexual partners of the same sex had a higher probability of having 5 or more same-sex partners respectively in the past year (WSW: 28.4% mutual masturbation, 27.8% oral sex; MSM: 36.2% mutual masturbation, 34.5% oral sex). Engagement with sex workers was reported by 4.7% (95% CI, 3.7-6.2%) of females and 18.1% (16.1-20.4%) of males, with higher odds among individuals with at least 5 partners in the past year (e.g., vaginal sex AOR = 7.40, 95% CI, 4.03-13.58). Self-reported STI positivity was 13.1%, associated with having at least 5 partners in the past year (e.g., vaginal sex AOR = 5.03, 95% CI, 1.44-17.61) and ever engaging with sex workers (e.g., vaginal sex AOR = 3.16, 95% CI, 1.67-5.99), but not with barrier protection frequency. Conclusions Patterns varied by sex, sexual orientation, and risk behaviours, underscoring the need for context-specific behavioural data to inform STI modelling and public health interventions.