Population size estimation of men who have sex with men in Hainan colleges based on geosocial networking App, South China

Background Men who have sex with men (MSM) have historically been a high-risk group for sexually transmitted diseases. In Hainan, the incidence of HIV and syphilis among MSM has increased rapidly. Additionally, there is a growing number of young students being diagnosed with HIV, with MSM identified as the primary demographic affected. However, the size of the MSM population within colleges and universities in Hainan Province, as well as the distribution of active MSM users, remains unknown. Methods In this study, the Blued App was employed to collect data on online users within Hainan colleges and universities from May 9 to May 18, 2023. A capture-recapture model was utilized to estimate MSM numbers, and uni-variate and geographic density analyses integrating survey data were used to uncover regional disparities among the MSM community at colleges and universities in Hainan. Results The findings indicated that the estimated MSM size in colleges across Hainan Province was 3130 (95%CI: 3025–3235), with 1833 (95%CI: 1754–1911) being active users. A questionnaire survey revealed that 89.28% of student MSM reported using the Blued App, and 57.14% of the individuals utilized it for seeking sexual partners. Among the 25 campuses in Hainan Province, A1 had the largest number of students using the Blued App, with a population size of 275 (95% CI:243–307), followed by A6 (207, 95%CI: 185–229). Among the male students, A2 (6.67%, 59/884) and A3 (6.16%, 130/2099) demonstrated a high proportion of MSM. A6 (47.04%, 119/253) and B2 (38.46%, 80/208) displayed a significant proportion of active users. Conclusions The proportion of MSM in male students of colleges across Hainan is moderate, with A City and B City identified as significant hotspots. Particular attention should be directed towards sexual health education, and sexually transmitted disease surveillance in specific colleges.