High Baseline Prevalence and Stable Incidence of Chlamydia and Gonorrhea During the First Year of HIV Pre-Exposure Prophylaxis: A Multicenter Italian Cohort Study

Introduction: – Concerns persist that HIV pre-exposure prophylaxis (PrEP) may be associated with increased sexually transmitted infections (STIs), but longitudinal data incorporating the pre-PrEP period and standardized screening remain limited. Methods: – We conducted a retrospective cohort study of individuals initiating oral emtricitabine/tenofovir disoproxil fumarate PrEP at 2 STI clinics in Milan, Italy (2018–2024). Participants underwent baseline and quarterly screening (pharyngeal, anal, vaginal swabs and urine nucleic acid amplification testing) for Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG). We estimated baseline prevalence and interval-specific conditional cumulative incidence across 0 to 3, 3 to 6, 6 to 9, and 9 to 12 months intervals, and described symptomatic and recurrent diagnoses. Finally, we evaluated STI trends across 3 calendar periods: 2018 to 2019, 2020 to 2021, and 2022 to 2024. Results: – A total of 1087 individuals were included (median age 35 years [interquartile ranges 30–41]); most were cisgender gay, bisexual, and other men who have sex with men (98.4%). At baseline, 15% (163/1,087) had at least one CT/NG infection. During follow-up, 516 new diagnoses occurred in 359 individuals (33%). Interval-specific conditional cumulative incidence for any CT/NG infection was 13.5%, 15.2%, 17.7%, and 12.7% across the 4 intervals. The majority of infections were asymptomatic. No substantial differences in STI trends were observed across the 3 calendar periods. Conclusions: – In this real-world PrEP cohort undergoing quarterly nucleic acid amplification testing screening, CT/NG diagnoses were common at baseline and maintained high but stable incidence during the first year after PrEP initiation, with no clear upward trend over time.