Quarterly screening optimizes detection of sexually transmitted infections when prescribing HIV preexposure prophylaxis.

Objective: The optimal screening frequency of sexually transmitted infections (STIs) for MSM and transgender women (TGW) on HIV pre-exposure prophylaxis (PrEP) is unclear, with present guidelines recommending screening every 3-6 months. We aimed to determine the number of STIs for which treatment would have been delayed without quarterly screening.

Design: The US PrEP Demonstration Project was a prospective, open-label cohort study that evaluated PrEP delivery in STI clinics in San Francisco and Miami, and a community health center in Washington, DC. In all, 557 HIV-uninfected MSM and TGW were offered up to 48 weeks of PrEP and screened quarterly for STIs.

Methods: The proportion of gonorrhea, chlamydia, and syphilis infections for which treatment would have been delayed had screening been conducted every 6 versus every 3 months was determined by taking the number of asymptomatic STIs at weeks 12 and 36 divided by the total number of infections during the study follow-up period for each STI.

Results: Among the participants, 50.9% had an STI during follow-up. If screening had been conducted only semiannually or based on symptoms, identification of 34.3% of gonorrhea, 40.0% of chlamydia, and 20.4% of syphilis infections would have been delayed by up to 3 months. The vast majority of participants (89.2%) with asymptomatic STIs reported condomless anal sex and had a mean of 8.1 partners between quarterly visits.

Conclusions: Quarterly STI screening among MSM on PrEP could prevent a substantial number of partners from being exposed to asymptomatic STIs, and decrease transmission.