Incidence and Predictors of HIV and Sexually Transmitted Infections Among Female Sex Workers and Their Intimate Male Partners in Northern Mexico: A Longitudinal, Multilevel Study.

Preventing human immunodeficiency virus (HIV) infection and other sexually transmitted infections (STIs) requires an understanding of sexual relationship factors beyond the individual level. We estimated HIV/STI incidence and identified time-varying predictors of STI acquisition in a prospective cohort study of female sex workers and their intimate (noncommercial) male partners in northern Mexico. From 2010 to 2013, couples underwent behavioral and biological assessments biannually for 24 months. Among 413 initially HIV-uninfected participants, 8 seroconverted during follow-up. Incidence of HIV (1.12 cases/100 person-years (PY)), chlamydia (9.47 cases/100 PY), active syphilis (4.01 cases/100 PY), and gonorrhea (1.78 cases/100 PY) was higher among women than among men (HIV: P = 0.069; all STIs combined: P < 0.001). In multivariable conditional logistic regression with individual fixed effects and correlated error terms within couples, risk of STI acquisition was significantly higher among women who had recently used cocaine, crack, or methamphetamine (adjusted odds ratio (OR) = 2.13, 95% confidence interval (CI): 1.07, 4.28). STI risk was lower among women who reported physically assaulting their male partners (adjusted OR = 0.44, 95% CI: 0.22, 0.86) and among men whose female partners had regular sex-work clients (adjusted OR = 0.38, 95% CI: 0.14, 1.03). Improving vulnerable couples' sexual health will require addressing the contexts in which drug use, interpersonal conflict, and economic vulnerability converge.