Effectiveness of a Pre-Exposure Prophylaxis Program on HIV Incidence and its Association with Syphilis: Retrospective Cohort Study at a Sexual Health Clinic in Beirut, 2022-2025

Abstract

Introduction: Pre-Exposure Prophylaxis (PrEP) is a cornerstone of HIV prevention, yet concerns remain regarding sexually transmitted infection trends and program retention. At SIDC, a sexual health clinic in Beirut, men who have sex with men (MSM) and trans-women (TW) are enrolled in a PrEP program that includes regular testing and follow-up. This study aims to compare the incidence of HIV and syphilis among PrEP users and non-users, identify factors associated with infection, examine determinants of PrEP initiation, and describe retention in the program.

Methods: This quasi-experimental retrospective longitudinal study included MSM and TW attending SIDC between January 2022 and December 2025. HIV and syphilis incidence rates and incidence rate ratios were estimated. Generalized Estimating Equations were used to identify factors, including current PrEP use, associated with first incident syphilis infection. Multivariable logistic regression was used to assess determinants of PrEP initiation. Retention patterns in the program were described.

Results: The analysis included 365 HIV-negative PrEP users and 2,780 HIV-negative non-users. The mean age at cohort entry was 29.4 years; 95.3% identified as cisgender men and 65.6% as homosexual. No incident HIV infections were observed among PrEP users (4,867 person-months), compared with an incidence rate of 11.2 per 10,000 person-months among non-users (9,793 person-months). Syphilis incidence was higher among PrEP users compared with non-users (IRR: 3.18, 95% CI: 1.56–6.73). This association remained after adjustment (aRR: 3.61, 95% CI: 1.65–7.88), with no other factors significantly associated with syphilis incidence. PrEP users were older, more educated, more likely to be engaged in healthcare, and reported higher-risk sexual behaviors. Retention in the program was limited, with 30.1% of PrEP users attending only the enrollment visit and a median follow-up duration of 10.4 months (IQR: 0–24.1).

Conclusion: No HIV infections were observed among PrEP users, consistent with PrEP effectiveness in this setting, while the higher observed incidence of syphilis may reflect differences in testing frequency and baseline risk profiles rather than a causal effect of PrEP use. These findings highlight the need to strengthen retention strategies and expand equitable access to PrEP, alongside integrating STI prevention and risk-reduction interventions within PrEP programs in Lebanon.