Four years of PrEP use; sexual behaviour and STIs in the AMPrEP demonstration project cohort among men who have sex with men in Amsterdam, the Netherlands

BackgroundAn increasing number of countries are currently implementing or scaling-up HIV pre-exposure prophylaxis (PrEP) care. With the introduction of PrEP, there was apprehension about possible risk compensation, particularly on the long term. 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. MethodsThe Amsterdam PrEP demonstration project (AMPrEP) provided oral daily PrEP and event-driven PrEP to MSM and transgender women in 2015-2020. 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 number of sex partners and condomless anal sex acts over time with casual partners (CAS) using negative binomial regression. We assessed changes in incidence rates (IR) of any STI (i.e., chlamydia, gonorrhoea, or infectious syphilis), individual STIs, and HIV over time using Poisson regression. Findings367 participants (365 MSM) commenced PrEP and were followed for a median 3.9 years (IQR=3.4-4.0). The number of sex partners decreased over time (adjusted rate ratio [aRR]=0.89/year, 95%CI=0.86-0.92), while the number of CAS acts with casual partners remained stable (aRR=0.98/year, 95%CI=0.94-1.01). IR of any STI was 87/100 person years (PY) (95%CI=82-93) and did not change over time for both daily PrEP or event-driven PrEP users. However, IRs of chlamydia and gonorrhoea decreased slightly in daily PrEP users. Two daily PrEP users, and no event-driven PrEP users, were diagnosed with HIV during their first year on PrEP. ConclusionWith no increase in the number of casual sex partners nor of CAS acts, we found no indication of possible risk compensation during the first four years of PrEP use. Although the STI incidence was high, it did not increase over time. FundingZonMw, RIVM, GGD, H-TEAM, Gilead.