Incidence of Syphilis Among People Using Hiv Pre-Exposure Prophylaxis (Prep)

Syphilis remains a highly relevant STI in public health, with marked growth in recent years. Although PrEP is effective in preventing HIV transmission, it does not protect against other STIs. Individuals on PrEP may adopt higher-risk sexual practices, favoring syphilis transmission. This study aimed to assess the incidence of syphilis during the first year of PrEP use. Cohort study analyzing clinical records of PrEP users followed at a specialized service, March 2022-June 2025. The primary outcome was syphilis diagnosis, considering prior history, diagnosis at enrollment, and incident cases during follow-up, based on serologic positivity and VDRL titer increases. Variables included sociodemographics, syphilis history, STI symptoms, VDRL and rapid-test results, and clinical diagnoses at subsequent visits every 3-4 months. Of 271 PrEP initiators, 179 (66.1%) returned for at least one visit, 111 (41.0%) for two, 72 (26.6%) for three, and 50 (18.5%) for four or more visits. Overall, 19.9% were ≤ 25 years; 87.7% cis men, 8.1% cis women, 4.2% trans women. By sexual orientation, 78.5% identified as homosexual, 11.5% heterosexual, and 10.0% bisexual. Most were single (89.7%), non-White (51.3%), and with income up to three minimum wages (64.1%). At enrollment, 41 (15.1%) reported a recent STI, 25 (9.2%) reported syphilis diagnosis in the previous six months, and 48 (17.7%) had a reactive rapid test for syphilis. At the second visit (N = 179), 6.4% had STI symptoms and 5.6% were diagnosed with active syphilis. STI symptoms were reported by 14.4%, 15.3%, and 14.0% at the third, fourth, and fifth visits, respectively; active syphilis was confirmed in 4.5%, 4.2%, and 4.0% at those visits. The study shows high prevalence and incidence of syphilis among PrEP users, reinforcing the need to intensify combination prevention with periodic testing, early diagnosis, timely treatment, and strengthened counseling within PrEP services.