Differences in substance use and sexual partnering between men who have sex with men, men who have sex with men and women and transgender women.

Men who have sex with men (MSM), men who have sex with men and women (MSM/W) and transgender women (TGW) remain the populations most severely and disproportionately impacted upon by HIV in Los Angeles County. Baseline data from community-based HIV-prevention programmes serving these populations were analysed to explore differences in demographic characteristics, substance use and sexual partnering between the three groups. Despite high HIV prevalence overall (MSM 34.7% versus MSM/W 16.1% versus TGW 21.9%, p < .001), there were striking differences in risk behaviours. Higher rates of homelessness were reported by MSM/W compared to MSM and TGW. Lower rates of education and less substance use were reported by TGW (62.2%), compared to MSM (79.7%) and MSM/W (92.6%). A much higher number of male sexual exchange partners were reported by TGW (MSM 1.04 [SD = 4.8] versus MSM/W 1.54 [SD = 10.3] versus TGW 12.37 [SD = 23.9], p < .001). Findings support the need for HIV-prevention interventions that specifically address the unique risk patterns among each population in order to curb HIV acquisition and transmission.