Original Contribution Incidence and Predictors of HIV and Sexually Transmitted Infections Among Female Sex Workers and Their Intimate Male Partners in Northern Mexico: A Longitudinal

Preventing human immunodeficiency virus (HIV) infection and other sexually transmitted infections (STIs) re-quires 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 behav-ioral and biological assessments biannually for 24 months. Among 413 initially HIV-uninfected participants, 8 sero-converted 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 termswithin couples, risk of STI acquisition was significantly higher amongwomen who had recently used cocaine, crack, or methamphetamine (adjusted odds ratio (OR) = 2.13, 95 % confidence in-terval (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. drug use; female sex workers; heterosexual couples; HIV; incidence; Mexico; prospective studies; sexuall