Aims To identify correlates of active syphilis infection among female sex workers (FSWs) in Tijuana and Ciudad Juarez.
Design Cross-sectional analyses of baseline interview data. Correlates of active syphilis (antibody titers >1 : 8) were identified by logistic regression.
Setting Tijuana and Ciudad Juarez, two Mexican cities on the US border that are situated on major drug trafficking routes and where prostitution is quasi-legal.
Participants A total of 914 FSWs aged ≥18 years without known human immunodeficiency virus (HIV) infection who had had recent unprotected sex with clients.
Measurements Baseline interviews and testing for syphilis antibody using Treponema pallidum particle agglutination (TPPA) and rapid plasma reagin (RPR) tests.
Findings Median age and duration in sex work were 32 and 4 years, respectively. Overall, 18.0% had ever injected drugs, 14.2% often or always used illegal drugs before or during sex in the past month, 31.4% had clients in the last 6 months who injected drugs, and 68.6% reported having clients from the United States. Prevalence of HIV and active syphilis were 5.9% and 10.3%, respectively. Factors independently associated with active syphilis included injecting drugs (AOR: 2.39; 95% CI: 1.40, 4.08), using illegal drugs before or during sex (AOR: 2.06; 95% CI: 1.16, 3.65) and having any US clients (AOR: 2.85; 95% CI: 1.43, 5.70).
Conclusions Among female sex workers in Tijuana and Ciudad Juarez, drug-using behaviors were associated more closely with active syphilis than were sexual behaviors, suggesting the possibility of parenteral transmission of T. pallidum. Syphilis eradication programs should consider distributing sterile syringes to drug injectors and assisting FSWs with safer-sex negotiation in the context of drug use.