Sexual behaviour and incidence of sexually transmitted infections among men who have sex with men (MSM) using daily and event-driven pre-exposure prophylaxis (PrEP): Four-year follow-up of the Amsterdam PrEP (AMPrEP) demonstration project cohort.

Background: An increasing number of countries are currently implementing or scaling-up HIV pre-exposure prophylaxis (PrEP) care. With the introduction of PrEP, there was apprehension that condom use would decline and sexually transmitted infections (STIs) would increase. To inform sexual health counselling and STI screening programmes, we aimed to study sexual behaviour and STI incidence among men who have sex with men (MSM) and transgender women who use long-term daily or event-driven PrEP. Methods and findings: The Amsterdam PrEP demonstration project (AMPrEP) was a prospective, closed cohort study, providing oral daily PrEP and event-driven PrEP to MSM and transgender women from 2015 to 2020. Participants could choose their PrEP regimen and could switch at each three-monthly visit. STI testing occurred at and, upon request, in-between 3-monthly study visits. We assessed changes in numbers of sex partners and condomless anal sex (CAS) acts with casual partners over time using negative binomial regression, adjusted for age. We assessed HIV incidence and changes in incidence rates (IRs) of any STI (i.e., chlamydia, gonorrhoea, or infectious syphilis) and individual STIs over time using Poisson regression, adjusted for age and testing frequency. A total of 367 participants (365 MSM) commenced PrEP and were followed for a median 3.9 years (interquartile range [IQR] = 3.4–4.0). Median age was 40 years (IQR = 32–48), 315 participants (85.8%) self-declared ethnicity as white and 280 (76.3%) had a university or university of applied sciences degree. Overall median number of sex partners (past 3 months) was 13 (IQR = 6–26) and decreased per additional year on PrEP (adjusted rate ratio [aRR] = 0.86/year, 95% confidence interval [CI] = 0.83–0.88). Overall median number of CAS acts with casual partners (past 3 months) was 10 (IQR = 3–20.5) and also decreased (aRR = 0.92/year, 95% CI = 0.88–0.97). We diagnosed any STI in 1,092 consultations during 1,258 person years, resulting in an IR of 87/100 person years (95% CI = 82–92). IRs of any STI did not increase over time for daily PrEP or event-driven PrEP users. Two daily PrEP users, and no event-driven PrEP users, were diagnosed with HIV during their first year on PrEP. Study limitations include censoring follow-up due to COVID-19 measures and an underrepresentation of younger, non-white, practically educated, and transgender individuals. Conclusions: In this prospective cohort with a comparatively long follow-up period of 4 years, we observed very low HIV incidence and decreases in the numbers of casual sex partners and CAS acts over time. Although the STI incidence was high, it did not increase over time. Trial registration: The study was registered at the Netherlands Trial Register (NL5413) https://www.onderzoekmetmensen.nl/en/trial/22706 Mark A. M. van den Elshout, Eline S. Wijstma and colleagues assess sexual behaviour and incidence of sexually transmitted infections among men who have sex with men using long-term daily and event-driven pre-exposure prophylaxis (PrEP) over a four-year period. Author summary: Why was this study done?: Oral pre-exposure prophylaxis (PrEP) is medication that almost 100% effectively prevents HIV when taken as prescribed: daily or before and after sex. Information on how people use PrEP, their sexual behaviour, and how often they acquire sexually transmitted infections (STI), can be used to tailor PrEP care to the needs of PrEP users. Since people can benefit from PrEP for several years (i.e., for as long as they are vulnerable to HIV), it is important to study the outcomes of PrEP use over longer periods of time. What did the researchers do and find?: Between 2015 and 2020, 365 men who have sex with men and 2 transgender women who were at risk for HIV in the Netherlands were provided oral PrEP and followed up every 3 months. We examined how participants use PrEP (daily or before and after sex), participants' sexual behaviour, and how often they tested positive for STIs or HIV, and whether these outcomes changed over 4 years of PrEP use. Over 4 years, most participants used PrEP correctly, and only 2 acquired HIV. The numbers of sex partners and anal sex acts without a condom with casual partners decreased over time, and STIs occurred frequently, but did not increase over time. What do these findings mean?: Our findings indicate that PrEP effectively prevents HIV over longer time periods and support structural implementation of PrEP with easy access. Our findings support regular counselling and STI testing as part of PrEP care. Young, non-white, practically educated, and transgender individuals were underrepresented in the study population; this should be considered when applying these findings to broader populations of PrEP users. [ABSTRACT FROM AUTHOR]