Modelling the effect of market forces on the impact of introducing human immunodeficiency virus pre-exposure prophylaxis among female sex workers.

Matthew Quaife,Fern Terris‐Prestholt,Zindoga Mukandavire,Peter Vickerman

doi:10.1002/hec.4211

Abstract

Pre-exposure prophylaxis (PrEP) to prevent human immunodeficiency virus (HIV) enables female sex workers (FSWs) to protect themselves from HIV without relying on clients using condoms. Yet, because PrEP reduces HIV risk, financial incentives to not use condoms may lead to risk compensation: reductions in condom use and/or increases in commercial sex, and may reduce the price of unprotected sex. In this analysis, we integrate market forces into a dynamic HIV transmission model to assess how risk compensation could change the impact of PrEP among FSWs and clients. We parameterise how sexual behavior may change with PrEP use among FSWs using stated preference data combined with economic theory. Our projections suggest the impact of PrEP is sensitive to risk compensatory behaviors driven by changes in the economics of sex work. Condom substitution could reduce the impact of PrEP on HIV incidence by 55%, while increases in the frequency of commercial sex to counter decreases in the price charged for unprotected sex among PrEP users could entirely mitigate the impact of PrEP. Accounting for competition between PrEP users and nonusers exacerbates this further. Alternative scenarios where increases in unprotected sex among PrEP users are balanced by decreases in non-PrEP users have the opposite effect, resulting in PrEP having much greater impact. Intervention studies need to determine how HIV prevention products may change the economics of sex work and provision of unprotected sex to enable a better understanding of their impact.

Highlights

QUAIFE ET AL.Female sex workers (FSWs) face a multitude of health risks including high rates of sexually transmitted infections (STIs) and human immunodeficiency virus (HIV) (Bekker et al, 2015)
We find that the impact of Pre‐exposure prophylaxis (PrEP) is highly sensitive to relatively small changes in condom use among non‐PrEP users as well as changes in the distribution of unprotected acts across PrEP users and nonusers resulting from risk compensation
Our analyses show that when the condom differential, and the effect of PrEP use on this premium, is large, the benefits of PrEP are reduced because there is a large incentive for PrEP users to increase their frequency of condom‐protected and condomless sex to maintain the same level of income

Summary

Introduction

Female sex workers (FSWs) face a multitude of health risks including high rates of sexually transmitted infections (STIs) and human immunodeficiency virus (HIV) (Bekker et al, 2015). The economic context of sex work means that FSWs can face strong price competition from other FSWs, alongside client resistance to condom use, including threats and use of violence (Beattie et al, 2010, Deering et al, 2014, Pronyk et al.; Wojcicki & Malala, 2001). A large body of economic research on sex work has shown that higher prices are associated with the provision of riskier sex; anecdotal evidence of compensating differentials in sex work has existed for years (Wojcicki and Malala, 2001), but it was not until the early‐2000s when Rao, Gupta, Lokshin, & Jana (2003) first empirically estimated a price premium of 79% for condomless sex among Indian FSWs, terming this the condom differential. Similar patterns have been seen in data from male sex workers, risks and market factors can differ substantively from FSWs, for example, there is a greater prevalence of non‐penetrative sex among male sex workers and penetrative sex is riskier through receptive anal sex (Galarraga et al, 2014)

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