The syndemic of incarceration, violence victimisation, needle/syringe sharing, & HIV infection: A population-based study of men who inject drugs in India.

Background & objectives Only a few studies to date have described how violence victimisation, incarceration experience, and needle/syringe sharing synergistically interact to increase HIV risk among people who inject drugs (PWID) in India. Methods We analysed cross-sectional data on 19,902 men who inject drugs, recruited in the 2014/15 Integrated Bio-Behavioural Surveillance study of India's National AIDS Control Organisation. The outcome was human immunodeficiency virus (HIV) status. Syndemic exposures included past-year incarceration, past-year severe physical violence victimisation, and needle/syringe sharing. Regression models included covariates such as age, education, marital status, inconsistent condom use, HIV knowledge, and HIV programme exposure. We tested interactions using linear probability (additive scale) and logistic (multiplicate scale) regression models and examined causal pathways via path analysis. Results In this study, the HIV prevalence was found to be 9.9 per cent among men who inject drugs. We estimated substantial rates of needle/syringe sharing (17.8%), past-year incarceration (10.2%), and severe violence victimisation (3.8%). Among those incarcerated, 28 per cent injected drugs in prison. HIV seropositivity was associated with needle/syringe sharing [Adjusted odds ratio (aOR)=1.33; 95% Confidence interval (CI), 1.08-1.63], but not with violence victimisation or incarceration. In the logistic regression models, a significant two-way interaction was found between needle/syringe sharing and violence victimisation (semi-elasticity=0.65; 95% CI, 0.01-1.29) and a three-way interaction between needle/syringe sharing, violence victimisation, and incarceration (semi-elasticity=1.86; 95% CI, 0.51-3.20). In the linear probability regression models, we estimated a three-way additive interaction (relative excess risk of interaction=0.21; 95% CI, 0.03-0.28). Using path analysis, we estimated statistically significant indirect effects of both incarceration (b=0.02; 95% CI 0.01, 0.03) and severe violence victimisation (b=0.01; 95% CI, 0.008 to 0.02) on the HIV status, operating through their effects on needle/syringe sharing. Interpretation & conclusions Incarceration, violence victimisation, and needle/syringe sharing synergistically interacted to magnify HIV risk among men who inject drugs. These findings suggest the presence of a syndemic. Integrated interventions addressing these co-occurring conditions (e.g., needle/syringe exchange in prisons, violence prevention) may be necessary to effectively reduce HIV transmission among PWID in India.