Comparison of trends in rates of sexually transmitted infections before vs after initiation of HIV preexposure prophylaxis among men who have sex with men

Importance: There have been concerns that HIV preexposure prophylaxis (PrEP) may be associated with increases in sexually transmitted infections (STIs) because of subsequent reductions in condom use and/or increases in sexual partners. Objective: To determine trends in STI test positivity among high-risk men who have sex with men (MSM) before and after the start of HIV PrEP. Design, Setting, and Participants: A before-after analysis was conducted using a subcohort of a single-group PrEP implementation study cohort in New South Wales, Australia (Expanded PreEP Implementation in Communities in New South Wales [EPIC-NSW]), from up to 1 year before enrollment if after January 1, 2015, and up to 2 years after enrollment and before December 31, 2018. STI testing data were extracted from a network of 54 sexual health clinics and 6 primary health care clinics Australia-wide, using software to deidentify, encrypt, and anonymously link participants between clinics. A cohort of MSM dispensed PrEP for the first time during the study, with 2 or more STI tests in the prior year and who tested during follow-up, were included from the EPIC-NSW cohort of HIV-negative participants with high-risk sexual behavior. Data analysis was performed from June to December 2019. Exposures: Participants were dispensed coformulated tenofovir disoproxil fumarate (300 mg) and emtricitabine (200 mg) as HIV PrEP. Main Outcomes and Measures: The main outcome was STI, measured using test positivity, defined as the proportion of participants testing positive for an STI at least once per quarter of follow-up. Outcomes were calculated for Chlamydia trachomatis and Neisseria gonorrhoea by site of infection (anorectal, pharyngeal, urethral, or any) and for syphilis. Results: Of the EPIC-NSW cohort of 9709 MSM, 2404 were included in the before-after analysis. The mean (SD) age of the participants was 36 (10.4) years, and 1192 (50%) were Australia-born. STI positivity was 52% in the year after PrEP (23.3% per quarter; 95% CI, 22.5%-24.2% per quarter) with no significant trend (mean rate ratio [RR] increase of 1.01 per quarter [95% CI, 0.99-1.02]; P = .29), compared with 50% positivity in the year prior to PrEP (20.0% per quarter [95% CI, 19.04%-20.95% per quarter]; RR for overall STI positivity, 1.17 [95% CI, 1.10-1.24]; P < .001), with an increase in quarterly STI positivity (mean RR of 1.08 per quarter, or an 8% increase per quarter [95% CI, 1.05-1.11]; P < .001; RR, 0.93 [95% CI, 0.90-0.96]; P < .001). Findings were similar when stratified by specific STIs and anatomical site. Conclusions and Relevance: STI rates were high but stable among high-risk MSM while taking PrEP, compared with a high but increasing trend in STI positivity before commencing PrEP. These findings suggest the importance of considering trends in STIs when describing how PrEP use may be associated with STI incidence.