PrEP users are under high risk of bacterial sexually transmitted infections. Sensitive and timely diagnostic strategies are crucial to allow rapid prescription of antimicrobial treatment. Several studies have shown that Chlamydia trachomatis (Ct) and Neisseria gonorrhea (Ng) screening at multiple anatomic sites may improve the diagnostic yield in high-risk populations.
In this retrospective cohort study, HIV-uninfected patients referred for PrEP were followed with periodic serologic testing of Syphilis (every 3 months) and culture/molecular testing of Ct/Ng (approximately every 6 months in asymptomatic patients; as needed for those with symptoms). We describe the baseline prevalence of Syphilis, Ct and Ng as well as the cumulative incidence of each infection at 6 and 12 months after PrEP initiation using Kaplan-Meier survival analysis. We also describe the frequency and percentage of Ct/Ng detection per anatomical site and calculate the percentage of missed diagnosis if molecular testing for Ct/Ng were applied only for symptomatic patients, or if screening is done in urine only.
386 PrEP users under follow-up in a single institution in Sao Paulo, Brazil, were included in the study. Most (94%) were men who have sex with men, with median age of 31 years old (interquartile range [IQR] 27-37). At baseline, active syphilis was detected in 23 participants (7%; 3 symptomatic and 20 latent or unknown stage), whereas Ct and Ng were detected in 9 patients each (8% and 9%) of whom only one Ng-positive patient had symptoms. After a median follow-up of 278 days (IQR 180-370), incident syphilis was detected in 24 PrEP users, with a cumulative incidence of 12% at 12 months; of those, 10 were symptomatic (3 in primary stage and 7 in secondary stage). Ct and Ng were detected in 13 patients and 10 patients, with a cumulative incidence of 12% and 10% at 12 months respectively. Had Ct/Ng molecular testing been used for symptomatic patients only, 15/16 (94%, 95% CI 70-100) cases would have been missed at baseline and 18/20 (90%; 95% CI 68-99) incident cases would have been missed. Had screening been performed in urine only, 12/16 (75%; 95%CI 48-93) cases would have been missed at baseline and 14/20 (70%; 95%CI 46-88) incident cases would have been missed.
Multiple anatomic site sampling is a powerful strategy to increment the diagnostic sensitivity of Ct/Ng molecular screening. This approach should be applied in high-risk PrEP users as to improve the capacity of accurate diagnosis and treatment.