Buffering syndemic effects in a sexual risk-reduction intervention for male clients of female sex workers: Results from a randomized controlled trial

Objectives. We sought to test the efficacy of a sexual risk intervention for male clients of female sex workers (FSWs) and examine whether efficacy was moderated by syndemic risk. Methods. From 2010 to 2014, we conducted a 2-arm randomized controlled trial (60-minute, theory-based, safer sex intervention versus a didactic timeequivalent attention control) that included 400 male clients of FSWs on the US- Mexico border with follow-up at 4, 8, and 12 months. We measured 5 syndemic risk factors, including substance use and depression. Primary outcomes were sexually transmitted infections incidence and total unprotected sex with FSWs. Results. Although participants in both groups became safer, there was no significant difference in behavior change between groups. However, baseline syndemic risk moderated intervention efficacy. At baseline, there was a positive association between syndemic risk and unprotected sex. Then at 12 months, longitudinal analyses showed the association depended on intervention participation (B = -0.71; 95% confidence interval [CI] = -1.22, -0.20; P = .007). Among control participants there still existed this modest association (B = 0.36; 95% CI = -0.49, 1.22; P = .09); among intervention participants there was a significant negative association (B = -0.35; 95% CI = -0.63, -0.06; P = .02). Conclusion. A brief intervention might attenuate syndemic risks among clients of FSWs. Other populations experiencing syndemic problems may also benefit from such programs.