Correlates of injection drug use among female sex workers in two Mexico–U.S. border cities

Objective To characterize the overlap between injection drug use and sex work by women in Tijuana and Cd. Juarez, situated on the Mexico–U.S. border. Methods FSWs aged ≥18 years who were not knowingly HIV-positive and reported having unprotected sex with ≥1 client in the prior 2 months underwent interviews and testing for HIV, syphilis, gonorrhea and Chlamydia. Logistic regression identified factors associated with injecting drugs within the last month. Results Of 924 FSWs, 18.0% had ever injected drugs. Among FSW-IDUs (N = 114), prevalence of HIV, syphilis titers ≥1:8, gonorrhea and Chlamydia was significantly higher at 12.3%, 22.7%, 15.2% and 21.2% compared to 4.8%, 13.1%, 5.2% and 11.9% among other FSWs (N = 810). FSW-IDUs also had more clients in the past 6 months (median: 300 versus 240, p = 0.02). Factors independently associated with injecting drugs in the past month included living in Tijuana, being younger, being married/common-law, longer duration in the sex trade, speaking English, earning less for sex without condoms, often using drugs before sex, and knowing other FSWs who injected drugs. Conclusions FSW-IDUs had higher STI levels, engaged in riskier behaviors and were more vulnerable to having unsafe sex with clients compared to other FSWs, indicating that this subgroup is an important bridge population requiring focused prevention.