OBJECTIVES: This study examined whether networks of drug-injecting and sexual relationships among drug injectors are associated with individual human immunodeficiency virus (HIV) serostatus and with behavioral likelihood of future infection. METHODS: A cross-sectional survey of 767 drug injectors in New York City was performed with chain-referral and linking procedures to measure large-scale (sociometric) risk networks. Graph-theoretic algebraic techniques were used to detect 92 connected components (drug injectors linked to each other directly or through others) and a 105-member 2-core within a large connected component of 230 members. RESULTS: Drug injectors in the 2-core of the large component were more likely than others to be infected with HIV. Seronegative 2-core members engaged in a wide range of high-risk behaviors, including engaging in risk behaviors with infected drug injectors. CONCLUSIONS: Sociometric risk networks seem to be pathways along which HIV travels in drug-injecting peer groups. The cores of large components can be centers of high-risk behaviors and can become pockets of HIV infection. Preventing HIV from reaching the cores of large components may be crucial in preventing widespread HIV epidemics.

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In a cross-sectional study of 174 new injecting drug users (IDUs) in New York City who had injected for < or = 6 years, we examined whether those who both share syringes and have personal risk networks that include high-risk injectors are particularly likely to be infected with HIV. Subjects were street recruited between July 1991 and January 1993, were interviewed about their risk behaviors in the prior 2 years and their personal risk networks with other IDUs in the prior 30 days, and were tested for HIV; 20% were HIV seropositive. Among those who both shared syringes and had a personal risk network member who injected more than once a day, 40% were HIV seropositive (versus 14% for others, p < 0.001). In simultaneous multiple logistic regression, the interaction of both sharing syringes and having a personal risk network member who injected more than once a day remained independently and significantly associated with being HIV seropositive (OR, 3.57; 95% CI, 1.22, 10.43; p < 0.020), along with Latino race/ethnicity and exchanging sex for money or drugs. These findings suggest that the combination of sharing syringes with having a high-risk personal network is a risk factor for HIV infection among new IDUs. Studies of risk factors for HIV infection among new IDUs and interventions to reduce the spread of HIV among them should focus on their risk networks as well as their risk behaviors.

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From 1988 to 1991, 6,882 drug injectors in 15 US cities were interviewed and had serum samples collected. The interviews and samples were analyzed for determination of significant predictors of human immunodeficiency virus (HIV) seroconversion in the 10 low seroprevalence cities and the five high seroprevalence cities. The unit of analysis was the period of observation between consecutive paired interviews/blood samples. In Cox proportional hazards regression, significant predictors of seroconversion in the low seroprevalence cities were: not being in drug treatment, injecting in outdoor settings or abandoned buildings, using crack cocaine weekly or more frequently, engaging in woman-to-woman sex, being of non-Latino race/ethnicity, and city seroprevalence. Predictors in high seroprevalence cities were: injecting with potentially infected syringes, not being in drug treatment, and having a sex partner who injected drugs. These findings suggest that HIV may be concentrated in sociobehavioral pockets of infection in low seroprevalence cities. For reducing HIV transmission, these results suggest: 1) in low seroprevalence cities, localized monitoring to detect specific emerging sociobehavioral pockets of infection, and quick implementation of appropriate targeted interventions if necessary; 2) in high seroprevalence cities, relatively more emphasis on locality-wide outreach and syringe-exchange projects to reduce risky behavior; and 3) in both types of cities, considerable expansion of drug treatment programs.