academic.oup.comSexually Transmitted Infections Among Men Who Have Sex With Men Using Daily and Event-Driven HIV Pre-Exposure Prophylaxis: A Retrospective Cohort StudyHIV pre-exposure prophylaxis (PrEP) has reduced HIV incidence among men who have sex with men (MSM), but bacterial sexually transmitted infections (STIs) remain common, with limited data comparing regimens.MethodsA retrospective cohort study was conducted at Melbourne Sexual Health Centre, Australia (2024–2025). MSM aged ≥18 reporting PrEP use (daily, event-driven, or switching) who were tested for chlamydia, gonorrhea, or syphilis were included. Positivity was assessed at first consultation (baseline); incidence was assessed among those with ≥2 tests ≥30 days apart. Logistic and Poisson regression estimated associations and incidence rate ratios.ResultsAmong 3229 PrEP users (median age 33, IQR 29–39), 51.0% were daily, 43.2% event-driven, and 5.8% switchers. At baseline, 33.7% (765/2268) had any STI, with lower positivity among event-driven users (29.8%) than daily users (37.0%) or switchers (37.6%; P = .001), primarily driven by differences in gonorrhea positivity. After adjustment, event-driven PrEP use was independently associated with lower odds of baseline STI positivity (aOR 0.75, 95% CI 0.62–0.90), while Medicare ineligibility and recent partners had higher odds. Over 700.6 person-years, any-STI incidence (39.4/100 person-years) did not differ across regimens.ConclusionsAlthough event-driven users had lower baseline STI positivity, incidence was similar across regimens, suggesting baseline differences reflect underlying risk profiles rather than ongoing risk.