The HIV epidemic in Thailand is concentrated in key populations, with the highest rates in men who have sex with men (MSM) and transgender women (TG). Previous studies of HIV incidence in these groups have been limited mostly to Bangkok. We measured HIV incidence in MSM and TG in four provinces and evaluated factors associated with incident infections to inform public health prevention efforts. An analysis was conducted using data collected during a prospective observational cohort study during April 2015-May 2018 in outpatient clinics in five hospitals across four provinces in Thailand. MSM and TG aged ≥18 years, who were not known to be HIV-infected, and who reported anal intercourse with a male or TG without a condom in the past six months were enrolled. Participants were followed-up every 6 months for 18 months with questionnaires and HIV testing. A total of 40 HIV seroconversions occurred during follow-up, resulting in an HIV incidence of 3.5 per 100 person-years (95% CI 2.5, 4.8). Multivariate analyses indicated that identifying as gay (adjusted hazard ratio [AHR] 4.9; 95% CI 1.7-14.2), having receptive anal sex in the past six months (AHR 3.6; 95% CI 1.4-9.5), using alcohol (AHR 3.3; 95% CI 1.3-8.3), and taking alkyl nitrites (AHR 4.4; 95% CI 1.7-11.2) in the past six months were all independently associated with HIV infection. Overall this study found a lower HIV incidence in the highest risk population in Thailand compared with similar studies in Bangkok. Accelerated prevention efforts are needed to make the goal of 'zero new infections' possible in Thailand.
