Syndemic and Synergistic Effects of Intimate Partner Violence, Crystal Methamphetamine, and Depression on HIV Sexual Risk Behaviors among Women Who Inject Drugs in Indonesia.

Women who inject drugs are disproportionately affected by co-occurring intimate partner violence (IPV), poor mental health, and substance use. Less is known about the potentially synergistic effects of these factors on women's HIV risk behavior, and no known studies in Asia examine these relationships. This study assessed the additive and interactive effects of exposure to syndemic IPV, depressive symptoms and non-injection crystal methamphetamine (crystal meth) on HIV sexual risk behaviors in the largest cross-sectional sample of women who inject drugs in Indonesia. Seven hundred thirty-one women aged ≥ 18 years, injecting drugs in the preceding 12 months, and residing in Greater Jakarta or Bandung, West Java, were recruited using respondent-driven sampling (RDS). Twenty-six percent of women experienced concurrent IPV, crystal meth use and depressive symptoms. In multivariate logistic regressions controlling for sociodemographic confounders, all three factors were significantly positively associated with sexual risk outcomes. In adjusted marginal effects models, concurrent experience of IPV, crystal meth use and depressive symptoms was associated with increases in the prevalence of HIV risk outcomes: STI symptomatology (from 12% to 60%), inconsistent condom use (from 3% to 22%), and engagement in survival sex work (from 6% to 25%). Statistically significant interaction was detected on both multiplicative and additive scales. Specifically, an interaction was observed on the multiplicative scale between depressive symptoms and crystal meth on STI symptomatology (OR = 2.61; 95% CI = 1.24, 5.48; p = 0.011). There was also evidence of additive interaction, with most observed joint effects being greater than additive. Specifically, significant positive interaction was observed between IPV and crystal meth on inconsistent condom use (AP = 0.38, p < 0.05); depressive symptoms and crystal meth on STI symptomatology (RERI = 2.04, p < 0.001; AP = 0.61, p < 0.001) and survival sex (RERI = 1.20, p < 0.01; AP = 0.53, p < 0.01); and IPV and depressive symptoms on STI symptomatology (RERI = 3.01, p < 0.01; AP = 0.52, p < 0.001; S = 2.70, p < 0.01) and survival sex (RERI = 1.21, p < 0.05; AP = 0.40, p < 0.05). This study provides new empirical evidence showing that the syndemic conditions of IPV, depressive symptoms and crystal meth consumption interact synergistically to increase women's HIV risk. Interventions that consider the full scope of syndemic vulnerabilities, rather than addressing individual conditions separately, may be essential.