Mechanisms through which drug, sex partner, and friendship network characteristics relate to risky needle use among high risk youth and young adults.

Drug injector social networks are a primary social space in which risky needle use behaviors associated with HIV transmission occur, but the mechanisms through which these social networks influence risky needle use are unclear. This study investigated two mechanisms, social support and social regulation, through which injection drug users' social networks might relate to risky needle use behaviors. We investigated how these mechanisms work in three types of social networks, namely, drug user, sex partner, and friendship networks. Data are from a study of HIV risk and protective behaviors of youth and young adults, ages 14-43, in the United States who were injection drug users and/or the sexual partners of users (N = 277). The three types of networks were constructed based on information respondents provided about their drug use partners, sexual partners, and friends. The networks were characterized by structural (i.e., size and density) and interactional (i.e., multiplexity and closeness) characteristics. We conducted tests for mediation using ordered probit models and multiple linear regression. In the drug networks, social regulation partially meditated the relationship between multiplexity and risky needle use (p<.10). In the sex partner networks, emotional support partially mediated the relationship between network size and risky needle use (p<.001), fully mediated the relationship between network closeness and risky needle use (p<.001), and partially mediated the relationship between multiplexity and risky needle use (p<.01). Mediators were not identified in the friendship networks. The findings demonstrate that network mechanisms explaining risky needle use differ for drug user and sex partner networks in ways consistent with the functional nature of each type of network tie.