Sexually transmitted infections incidence in young Thai men who have sex with men and transgender women using HIV pre-exposure prophylaxis.

Background: Sexually transmitted infections are a major public health issue worldwide. HIV pre-exposure prophylaxis (PrEP) use among youth may be associated with increased incidence of sexually transmitted infections (STIs).
Objectives: To measure the prevalence and incidence of STIs among young men who have sex with men (YMSM) and young transgender women (YTGW) using PrEP.
Methods: A prospective cohort of 15- to 19-year-old YMSM and YTGW with HIV risk defined as inconsistent condom use and/or multiple sex partners were enrolled. Participants were provided daily oral tenofovir disoproxil fumarate/emtricitabine. STI screening was done at baseline and month 6 for syphilis, urine, and anal swab nucleic acid amplification testing for C. trachomatis (CT) and N. gonorrheaoe (NG).
Results: From March 2018 to June 2019, 200 adolescents (147 MSM and 53 TGW) with a median (IQR) age of 18 years (17-19) were enrolled. STI prevalence was 22.5% (95% CI 16.7-28.3). STI incidence was 25.2 per 100 person-years (95% CI 14.7, 40.3). Factors associated with STI incidence were self-reported >2 sex partners in the past month (unadjusted rate ratio [uRR] 4.6, 95% CI 1.0, 20.6), and moderate PrEP adherence (uRR 7.3, 95% CI 1.6, 32.6).
Conclusions: STI incidence in YMSM and YTGW PrEP users was high at approximately one in five. Regular screening and treatment of STIs should be implemented in youth HIV prevention packages.