Prevalence and Determinants of Sexually Transmitted Infections Among Thai Men Who Have Sex with Men Enrolled in National Pre-Exposure Prophylaxis Program: A Real-World Cross-sectional Study.

BACKGROUND: Sexually transmitted infections (STIs) remain a major public health concern among men who have sex with men (MSM). This study estimated STI prevalence and associated factors among MSM enrolled in Thailand's national pre-exposure prophylaxis (PrEP) registry under the Universal Health Coverage (UHC) program. METHODS: We conducted a cross-sectional analysis of MSM aged 15-49 years who underwent STI testing between January 2020 and August 2024 at enrolment in the PrEP registry program. STIs included syphilis, gonorrhoea, chlamydia and chancroids. Multivariable logistic regression was used to identify factors associated with STI and syphilis. RESULTS: Among 24,606 MSM, 1,974 (8.0%) were diagnosed with any STI, predominantly syphilis (n=1,911; 7.7%). STI prevalence was highest among MSM aged 20-24 years (8.6%) followed by 35-49 years (8.7%). STI prevalence was higher among those with prior PrEP use (9.7%) than among non-users (7.7%) and was markedly elevated among HCV-positive MSM (24.0%). In multivariable models, higher odds of STI diagnosis were observed among MSM aged 20-24 years (adjusted odds ratio [aOR] 1.21; 95% CI 1.08-1.36) and 35-49 years (aOR 1.14; 95% CI 1.01-1.29), those with prior PrEP use (aOR 1.26; 95% CI 1.11-1.45), and those with hepatitis C virus infection (aOR 3.17; 95% CI 1.95-5.13). CONCLUSIONS: STIs, particularly syphilis, remain common among MSM enrolled in Thai national PrEP program. These findings highlight the need to integrate STI and hepatitis screening into PrEP services and to strengthen targeted prevention strategies for MSM at increased risk.