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 two STI clinics in Milan, Italy (2018-2024). Participants underwent baseline and quarterly screening (pharyngeal, anal, vaginal swabs and urine NAATs) for Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG). We estimated baseline prevalence and interval-specific conditional cumulative incidence (CCI) across 0-3, 3-6, 6-9, and 9-12 months intervals, and described symptomatic and recurrent diagnoses. Finally, we evaluated STI trends across three calendar periods: 2018-2019, 2020-2021, and 2022-2024. RESULTS: A total of 1,087 individuals were included (median age 35 years [IQR 30-41]); most were cisgender GBMSM (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 CCIs for any CT/NG infection were 13.5%, 15.2%, 17.7%, and 12.7% across the four intervals. The majority of infections were asymptomatic.No substantial differences in STI trends were observed across the three calendar periods. CONCLUSIONS: In this real-world PrEP cohort undergoing quarterly NAAT 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.