Rethinking approaches to risk reduction for injection drug users: differences in drug type affect risk for HIV and hepatitis C virus infection through drug-injecting networks.

OBJECTIVE: To identify and compare the drug-injecting network characteristics of cocaine and heroin injectors associated with a risk of HIV and hepatitis C virus (HCV).

METHODS: Active injectors were recruited from syringe exchange and methadone programs. Characteristics of all participants and their social networks were elicited. Regression analysis using generalized estimating equations examined the network characteristics of injection drug users (IDUs) relative to cocaine or heroin use in the past 6 months.

RESULTS: Of 282 IDUs, 228 (81%) used cocaine and 54 (19%) used heroin as their primary injected drug. In analyses adjusted for age and gender, cocaine injectors compared with heroin injectors were more likely to live in unstable housing (odds ratio [OR] = 3.55, 95% confidence interval [CI]: 1.49 to 8.40), self-report HCV infection (OR = 4.69, 95% CI: 2.14 to 10.31), and have a greater number of IDUs in their social network (OR = 1.61, 95% CI: 1.14 to 2.28) and were less likely to be polydrug users (OR = 0.06, 95% CI: 0.02 to 0.16) and to have social support (OR = 0.97, 95% CI: 0.95 to 0.99). The injecting networks of cocaine users were more likely to have members who were older (OR = 1.08, 95% CI: 1.04 to 1.12), had a history of shooting gallery use (OR = 2.27, 95% CI: 1.08 to 4.76), and had shorter relationships with the subject (OR = 0.91, 95% CI: 0.85 to 0.97).

CONCLUSIONS: Beyond personal behaviors, HIV and HCV infection risk seems to be linked to social network traits that are determined by drug type. Prevention efforts to control the spread of bloodborne viruses among IDUs could benefit from tailoring interventions according to the type of drug used.