Change in sexual risk behaviour after 6 months of pre-exposure prophylaxis use: results from the Amsterdam pre-exposure prophylaxis demonstration project.

OBJECTIVE: HIV pre-exposure prophylaxis (PrEP) use may lead to higher STI incidence via behavioural risk compensation. We examined changes in sexual behaviour between baseline and 6 months after PrEP initiation among MSM and transgender women (TGW). DESIGN: Prospective, open-label demonstration study at a large sexually transmitted infection (STI) clinic in Amsterdam, the Netherlands. METHODS: Participants answered questions about sexual behaviour in the preceding 3 months, including number of anal sex partners and frequency of anal sex with and without condom by partner type and were tested for STI. Sexual behaviour at baseline was compared with 6 months after PrEP initiation using Wilcoxon signed rank tests. Logistic regression was used to identify factors associated with an increase in receptive condomless anal sex acts (rCASa) with casual partners. RESULTS: Data were available for 328 (99%) MSM and 2 (1%) TGW. The number of receptive and insertive condomless anal sex acts (CASa) increased (baseline: median 11, interquartile range 4-23; 6 months: median 14, interquartile range 6-26, P < 0.001), whereas the number of anal sex partners (P = 0.2) and anal sex acts (P = 0.8) remained unchanged. Prevalence of STI was stable. Older age, prior engagement in chemsex, recent use of postexposure prophylaxis and choosing a daily PrEP regimen at baseline were associated with an increase in rCASa with casual partners. CONCLUSION: Over the first 6 months after initiation of PrEP, an increase in insertive and receptive CASa with casual partners was observed. Long-term follow-up data are needed and STI incidence needs to be closely monitored.