Violence, trauma and living with HIV: Longitudinal predictors of initiating crystal methamphetamine injection among sex workers

Background: Despite rapid increases in crystal methamphetamine (CM) use worldwide and established gendered patterns of use, empirical research on CM injection initiation among sex workers is limited. Given the wide range of harms associated with CM, alongside stimulant effects including sexual dis-inhibition and prolonged awakeness, this study aimed to longitudinally investigate socio-structural predictors of initiating CM injection among sex workers in Vancouver, Canada. Methods: Data (2010-2014) were drawn from a community-based cohort of women sex workers: AESHA (An Evaluation of Sex Workers Health Access). Participants completed bi-annual interviewer-administered questionnaires and HIV/STI testing. Kaplan Meier methods and Cox proportional hazards regression were used to model predictors of CM injection initiation among CM injection-naive participants. Results: Of 455 participants eligible at baseline, 14.3% (n = 65) injected CM for the first time over follow-up, with an incidence density of 6.79 per 100 person-years (95% Confidence Interval [CI] 5.30-8.69). In multivariable analysis, injection heroin use (Adjusted Hazard Ratio [AHR] 6.11; 95%CI 3.24-11.52), having an intimate partner who injects-drugs (AHR 2.93; 95%CI 1.57-5.46), workplace violence (AHR 2.85; 95%CI 1.74-4.67), HIV seropositivity (AHR 2.69; 95%CI 1.45-5.00), and childhood abuse (AHR 1.86; 95%CI 0.99-3.49) were independently associated with initiating CM injection. Conclusions: Findings underscore the gendered and social risk environment of CM injection initiation among sex workers. The strong influences of historical/workplace violence, coupled with heroin injection (known to be self medicating for post-traumatic stress) as a primary risk pathway, emphasize the urgency of increasing access to integrated, trauma-informed addiction treatment and HIV care for marginalized women.