HIV pre-exposure prophylaxis (PrEP) use may lead to higher STI incidence via behavioral risk compensation. We examined changes in sexual behaviour between baseline and six months after PrEP initiation among men who have sex with men (MSM) and transgender women (TGW).
Prospective, open-label demonstration study at a large sexually transmitted infections (STI) clinic in Amsterdam, the Netherlands.
Participants answered questions about sexual behaviour in the preceding three 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 six 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.
Data were available for 328 (99.4%) MSM and 2 (0.6%) TGW. The number of receptive and insertive condomless anal sex acts (CASa) increased (baseline: median 11, IQR 4-23; 6 months: median 14 IQR 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 post-exposure prophylaxis and choosing a daily PrEP regimen at baseline were associated with an increase in rCASa with casual partners.
Over the first six 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.