Application of the "syndemics" theory to explain unprotected sex and transactional sex: A crosssectional study in men who have sex with men (MSM), transgender women, and non-MSM in Colombia.

Introduction: Men who have sex with men (MSM) and transgender women (TW) in Colombia are highly affected by HIV. To improve understanding of the role of HIV risk behaviors in HIV acquisition, we used the syndemic framework, a useful concept to inform prevention efforts. Objective: To examine the effect of four psychosocial conditions, namely, forced sex, history of childhood sexual abuse, frequent alcohol use, and illicit drug use on unprotected sex and the synergistic effects ("syndemic" effects) of these conditions on HIV risk behavior. Materials and methods: We enrolled a total of 812 males (54.7% men who have sex with men, MSM; 7.3% transgender women, and 38% non-MSM). The participants were recruited from neighborhoods of low socioeconomic status through free HIV-counseling and -testing campaigns. We performed Poisson regression analysis to test the associations and interactions between the four psychosocial conditions and unprotected sex with regular, occasional, and transactional partners. To test the "syndemic" model, we assessed additive and multiplicative interactions. Results: The prevalence of any psychosocial condition was 94.9% in transgender women, 60.1% in MSM, and 72.2% in non-MSM. A higher likelihood of transactional sex was associated in MSM (prevalence ratio (PR)=7.41, p<0.001) and non-MSM (PR=2.18, p<0.001) with three or all four conditions compared to those with one condition. Additive interactions were present for all combinations of psychosocial problems on transactional sex in MSM. No cumulative effect or additive interaction was observed in transgender women. Conclusions: Our study highlights the need for bundled mental health programs addressing childhood sexual abuse, illicit drug use, and frequent alcohol use with other HIV prevention programs.