Clinical Infectious Diseases | July 2017
Background: Preexposure prophylaxis (PrEP) is highly effective for preventing HIV, but risk compensation (RC) in men who have sex with men (MSM) raises concerns about increased sexually transmitted infections (STIs). CDC’s PrEP guidelines recommend biannual STI screening, which may reduce incidence by treating STIs that would otherwise remain undiagnosed. We investigated the impact of these two potentially counteracting phenomena.
Methods: With a stochastic network-based mathematical model of HIV and rectal/urogenital Neisseria gonorrhoeae (NG) and Chlamydia trachomatis (CT) transmission dynamics among MSM in the United States, we simulated PrEP uptake following the prescription indications and HIV/STI screening recommendations in the CDC guidelines. Model scenarios varied PrEP coverage (the proportion of MSM indicated for PrEP who received it), RC (as a reduction in the per-act probability of condom use), and the STI screening interval.
Results: In our reference scenario (40% coverage, 40% RC), 42% of NG and 40% of CT infections would be averted over the next decade. A doubling of RC would still result in net STI prevention relative to no PrEP. STIs declined because PrEP-related STI screening resulted in a 17% and 16% absolute increase in the treatment of asymptomatic and rectal STIs, respectively. Screening and timely treatment at quarterly vs biannual intervals would reduce STI incidence a further 50%.
Conclusions: Implementation of the CDC PrEP guidelines while scaling up PrEP coverage could result in a significant decline in STI incidence among MSM. Our study highlights the design of PrEP not only as antiretroviral medication, but as combination HIV/STI prevention incorporating STI screening.