Effect of pre-exposure prophylaxis on risky sexual behaviour of female sex workers in Dakar, Senegal: A randomised controlled trial
Authors: Toh Wally , Lépine Aurelia , Gueye Khady , Fall Mame Mor , Diop Abdou Khoudia , Mbaye El hadji Alioune , Ndour Cheikh Tidiane , O’donnell Owen 
Published: August 2024

AbstractBackgroundHIV prevention through pre-exposure prophylaxis (PrEP) may encourage riskier sexual behaviours that undermine the protection afforded by PrEP and generates negative spillovers on sexually transmitted diseases. Tests for such risk compensatory behaviour in high-risk populations, such as the female sex workers (FSW) in Senegal we studied, are lacking.MethodsWe stratified the sample by self-reported sexual risk-taking and prior PrEP experience and randomly assigned them to PrEP referral in October 2021-January 2022 (treatment, n=300) or to deferred PrEP referral after the endline survey in April-May 2022 (control, n=200). We randomised 500 FSWs to start PrEP and included 308 FSWs in the final analysis (T=182, C=126). We compared outcomes in the period preceding PrEP referral of the control group. The primary outcome was self-reported condom use with clients. Secondary outcomes were self-reported sexual risk taking, number of clients, proportion of regular clients, perceived HIV risk of clients, and type of sex act. We estimated intention-to-treat effects of PrEP referral and both average treatment effects on the treated and local average treatment effects of PrEP utilisation. The trial is registered with ISRCTN (ISRCTN16445862).FindingsPrEP referral increased the probability of using PrEP by 34.5 percentage points (pp) [95% CI: 25.4, 43.6; p<0.0001, control group mean: 11.1%]. Estimated effects of PrEP referral and PrEP use on condom use with the last client were 3.3 pp [95% CI: -4.0, 10.6; p=0.376] and 7.9 pp [95% CI: -10.4, 26.3; p=0.397 respectively (control group mean: 84.9%). When looking at condom use with all last three clients, these effects were 11.0 pp [95% CI: 0.8, 21.1; p=0.034] and 25.8 [95% CI: 5.2, 46.4] respectively (control group mean: 67.5%) There were no notable effects on other risky behaviours.InterpretationThis randomised experiment did not give strong grounds for concerns that PrEP encouraged sexual risk-taking by FSWs, at least in the short-term. Robustness of this finding should be tested in larger, longer-term studies and in other contexts. Whether PrEP users are more likely to overreport condom use than non-PrEP users should also be further investigated.FundingMRC Public Health Intervention Development Scheme from UKRI and D.P. Hoijer Fonds, Erasmus Trustfonds, Erasmus University Rotterdam, The Netherlands.Research in contextEvidence before this studyPre-exposure prophylaxis (PrEP) is becoming an essential part of HIV prevention among high-risk populations in low-and middle-income countries. However, compensatory risky behaviour may partially offset the protection PrEP gives against HIV and may increase the prevalence of other sexually transmitted diseases. Risk compensation may exhibit more strongly among female sex workers (FSWs) as condomless sex is better renumerated. We searched PubMed in January 2024 using the terms (prep) AND (female sex workers) AND (randomised controlled trial) (28 search results) and (PrEP) AND (risk compensation) (140 search results). We did not find any randomised controlled trial testing whether PrEP uptake impacts the prevalence of unprotected sex amongst FSWs. For men who have sex with men, the evidence was mixed, with risk compensation evident in more recent studies.Added value of this studyTo our knowledge, this study provides the first evidence from a randomised experiment on whether PrEP causes compensatory risky sexual behaviour by FSWs. We found no strong evidence that either PrEP referral or PrEP use reduces condom use or increases measures of sexual risk-taking. Conversely, we found that PrEP users believe that PrEP is more effective when used with condoms.Implications of all the available evidenceIt is generally believed that prescribing PrEP to populations at high risk of HIV infection improves HIV prevention, despite some offsetting risk compensation, but may have a negative impact on the control of other sexually transmitted infections. Our study, which should be replicated with larger samples and in other contexts, suggests that concerns about a negative spillover effect of PrEP on risky sexual behaviour of FSWs may not be well founded. However, this could change if beliefs about dependence of PrEP effectiveness on complementary condom use were to change.