Effect of pre-exposure prophylaxis on risky sexual behaviour of female sex workers in Dakar, Senegal: A randomised controlled trial

Background HIV prevention through pre-exposure prophylaxis (PrEP) may encourage riskier sexual behaviours that undermine the protection afforded by PrEP and generate negative spillovers through sexually transmitted infections (STIs). Tests for such risk compensatory behaviour in high-risk populations, such as female sex workers (FSWs), are lacking. This study aims to assess whether risk compensatory behaviours were observed among FSWs in Senegal after the rollout of PrEP. 

Methods and findings In a randomised controlled trial with a Zelen design, we stratified FSWs in Dakar (Senegal) by self-reported sexual risk-taking and prior PrEP experience and randomly assigned them to immediate referral for oral PrEP (Treatment) from 7 September 2021 to end January 2022 or delayed PrEP referral (Control). We compared outcomes 3–8 months after the referral of the treatment group and before the referral of the control group. Primary outcomes were self-reported condom use with clients and perceived HIV/STI risks from sex with clients with and without a condom. The analysis is a modified intention-to-treat analysis. We estimated effects of PrEP referral as well as effects of oral PrEP use induced by randomised assignment to active PrEP referral. Out of 500 individuals randomised, 308 (61.6%) were included in the analysis (Treatment: 182/300=60.7%; Control: 126/200=63%). PrEP referral increased the probability of using oral PrEP by 34.5 percentage points (pp) (95% CI [25.4, 43.6]; p<0.001). Estimated effects of PrEP referral and PrEP use on condom use with the last client were positive but not statistically significantly different from zero. PrEP referral was estimated to increase the probability of condom use with all of the last three clients by 11.0 pp (95% CI [0.8, 21.2]; p=0.034). PrEP use was estimated to increase this probability by 25.8 pp (95% CI [5.2, 46.4]; p=0.014). Main limitations were low power, high attrition, self-reported outcomes and a limited follow-up period. 

Conclusions This study, conducted in one location, did not find evidence that PrEP referral or oral PrEP use increased self-reported risky sex behaviours of FSWs within 3–8 months. The robustness of this finding needs to be tested with larger cohorts followed for longer periods in other settings, and using survey instruments that allow further examination of whether PrEP users are more likely to overreport condom use.