Characterizing the drug-injecting networks of cocaine and heroin injectors in Montreal.

BACKGROUND There is little understanding about how the social networks of cocaine injectors are different from those of heroin users and about how such differences are associated with injection risk behaviours. Therefore, the objective of this study was to compare drug-injecting network characteristics of cocaine and heroin injectors believed to be associated with a risk of bloodborne infections. METHODS Active injection drug users (IDUs) were recruited between April 2004 and January 2005 from three syringe exchange and two methadone treatment programs in Montreal, Canada. Characteristics of each participant and of up to 10 social network members (IDU and non-IDU) with whom frequent contact had occurred in the past month were elicited using a structured, interviewer-administered questionnaire. The current analysis focussed on the drug-injecting network members. Logistic regression was used to examine network characteristics in relation to cocaine and heroin injection. RESULTS Of 282 study subjects, 81% used cocaine and 19% used heroin as their primary injected drug in the past 6 months. Compared to heroin injectors, participants who injected cocaine had lower odds of knowing their network members for a longer time (OR=0.92, 0.85-0.99), were more likely to report a larger IDU network (OR=1.64, 1.18-2.29) and have IDU partners who had a history of attending shooting galleries (OR=2.42, 1.05-5.56). INTERPRETATION This study identified high-risk network-related factors associated with bloodborne infections in cocaine injectors. Prevention efforts may benefit from tailoring interventions according to type of drug used, with particular attention to the drug injecting-network of IDUs.