SEXUAL BEHAVIOR AND STI INCIDENCE DURING THE FIRST 4 YEARS OF PrEP USE AMONG MSM

ABSTRACT

Background: A prospective demonstration project in Amsterdam (AMPrEP) provided pre-exposure prophylaxis (PrEP) to people vulnerable to HIV in 2015- 2020. Data on long-term trends in sexual behavior and incidence of STIs during PrEP use are needed to inform future PrEP programs. Therefore, we assessed sexual behavior and incidence rates of STIs among MSM and transgender women on PrEP over four years. Method(s) AMPrEP participants chose between oral PrEP daily (dPrEP) or event-driven (edPrEP) at baseline and could switch regimens at each 3-monthly study visit. They were tested for STIs at these visits and if necessary in between. Follow-up began at PrEP initiation and continued until 48 months of follow-up or was censored at March 15, 2020 (start COVID-19), whichever occurred first. We assessed changes over time in incidence rates (IR) of chlamydia, gonorrhea, and infectious syphilis using Poisson regression. We estimated the IR of Hepatitis C (HCV) diagnoses per consecutive year. We described the number of HIV diagnoses, and sexual behavior (i.e. number of sex partners, condomless anal sex acts with casual partners [CAS]). Result(s) A total of 367 (365 MSM) started PrEP and contributed 1249 person-years of observation. IRs of any STI was 87[95%CI 82-93]/100PY. There was no change in the IR of any STI and infectious syphilis over time on PrEP. We observed a slight decrease in incident chlamydia and gonorrhea in daily PrEP users (Table). Two incident HIV cases were diagnosed in the first year of follow-up. IRs for HCV were 1.5[0.6-3.6], 2.5[1.3-5.0], 0.7[0.2-2.7], and 0.4[0.1- 2.8]/100PY, per consecutive year on PrEP. Median number of sex partners per 3-month period decreased from 16[IQR 8-34] and 12[6-25] (dPrEP and edPrEP, respectively) at baseline, 15[7-30] and 8[3-16] at 24 months, and 12[6-26] and 5[2-12] at 48 months. Median number of CAS acts with casual partners were respectively 7[3-15] and 4[1-9] at baseline, 14[5-25] and 4[1-12] at 24 months, and 12[4-25] and 4[1-9] at 48 months. Conclusion(s) Over the first 4 years of PrEP use overall STI incidence was high and stable. Chlamydia and gonorrhea incidence declined slightly in daily users. Numbers of sex partners seemed to decrease in both dPrEP and edPrEP users. Number of CAS acts with casual partners appeared to increase first, and then stabilized. Notably, this did not result in increased incidence of STIs. Regular testing and treatment of STIs remain a priority among PrEP users. Biomedical prevention of STIs can be examined in this context.