Faculty Bibliography

In the United States, people who inject drugs continue to be at greatly increased risk of HIV infection. To estimate the effectiveness of various prevention scenarios, we modeled HIV transmission in a dynamic network of drug users and people who did not use drugs that was based on the New York Metropolitan Statistical Area population. We compared the projected HIV incidence in 2020 and 2040 if current approaches continue to be used to the incidence if one or more of the following hypothetical interventions were applied: increased HIV testing, improved access to substance abuse treatment, increased use of needle and syringe programs, scaled-up treatment as prevention, and a "high impact" combination scenario, consisting of all of the strategies listed above. No strategy completely eliminated HIV transmission. The high-impact combination strategy produced the largest decrease in HIV incidence-a 62 percent reduction compared to the status quo. Our results suggest that increased resources for and investments in multiple HIV prevention approaches will be required to eliminate HIV transmission among people who inject drugs.

OBJECTIVES/OBJECTIVE:We estimated race/ethnicity-specific incident AIDS diagnosis rates (IARs) among people who inject drugs (PWID) in U.S. metropolitan statistical areas (MSAs) over time to assess the change in disparities after highly active antiretroviral therapy (HAART) dissemination. METHODS:We compared IARs and 95% confidence intervals (CIs) for black/African American and Hispanic/Latino PWID with those of white PWID in 93 of the most populous MSAs. We selected two three-year periods from the years immediately preceding HAART (1993-1995) and the years with the most recent available data (2005-2007). To maximize stability, we aggregated data across three-year periods, and we aggregated data for black/African American and Hispanic/Latino PWID for most comparisons with data for white PWID. We assessed disparities by comparing IAR 95% CIs for overlap. RESULTS:IARs were significantly higher for black/African American and Hispanic/Latino PWID than for white PWID in 81% of MSAs in 1993-1995 and 77% of MSAs in 2005-2007. MSAs where disparities became non-significant over time were concentrated in the West. Significant differences were more frequent in comparisons between black/African American and white PWID (85% of MSAs in 1993-1995, 79% of MSAs in 2005-2007) than in comparisons between Hispanic/Latino and white PWID (53% of MSAs in 1993-1995, 56% of MSAs in 2005-2007). IARs declined modestly across racial/ethnic groups in most MSAs. CONCLUSIONS:AIDS diagnosis rates continue to be substantially higher for black/African American and Hispanic/Latino PWID than for white PWID in most large MSAs. This finding suggests a need for increased targeting of prevention and treatment programs, as well as research on MSA-level conditions that may serve to maintain the disparities.

This pilot study explores the feasibility and preliminary efficacy of the Staying Safe Intervention, an innovative, strengths-based program to facilitate prevention of infection with the human immunodeficiency virus and with the hepatitis C virus among people who inject drugs (PWID). The authors explored changes in the intervention's two primary endpoints: (a) frequency and amount of drug intake, and (b) frequency of risky injection practices. We also explored changes in hypothesized mediators of intervention efficacy: planning skills, motivation/self-efficacy to inject safely, skills to avoid PWID-associated stigma, social support, drug-related withdrawal symptoms, and injection network size and risk norms. A 1-week, fivesession intervention (10 hours total) was evaluated using a pre- versus 3-month posttest design. Fifty-one participants completed pre- and posttest assessments. Participants reported significant reductions in drug intake and injection-related risk behavior. Participants also reported significant increases in planning skills, motivation/self-efficacy, and stigma management strategies, while reducing their exposure to drug withdrawal episodes and risky injection networks.

PURPOSE: We focus on a little-researched issue-how human immunodeficiency virus (HIV) epidemics and programs in key populations in metropolitan areas affect epidemics in other key populations. We consider (1) How are earlier epidemics among people who inject drugs (PWID) and men who have sex with men (MSM) related to later AIDS incidence and mortality among heterosexuals?; (2) Were prevention programs targeting PWID or MSM associated with lower AIDS incidence and mortality among heterosexuals?; and (3) Was the size of the potential bridge population of noninjecting drug users (NIDUs) in a metropolitan area associated with later AIDS incidence and mortality among heterosexuals? METHODS: Using data for 96 large U.S. metropolitan areas, Poisson regression assessed associations of population prevalences of HIV-infected PWID and MSM (1992); NIDU population prevalence (1992-1994); drug use treatment coverage for PWID (1993); HIV counseling and testing coverage for MSM and for PWID (1992); and syringe exchange presence (2000) with CDC data on AIDS incidence and mortality among heterosexuals in 2006-2008, with appropriate socioeconomic controls. RESULTS: Population density of HIV+ PWID and of NIDUs were positively related, and prevention programs for PWID negatively related to later AIDS incidence among heterosexuals and later mortality among heterosexuals living with AIDS. HIV+ MSM population density and prevention programs for MSM were not associated with these outcomes. CONCLUSIONS: Efforts to reduce HIV transmission among PWID and NIDUs may reduce AIDS and AIDS-related mortality among heterosexuals. More research is needed at metropolitan area, network, and individual levels into HIV bridging across key populations and how interventions in one key population affect HIV epidemics in other key populations.

In 2001, Friedman et al. conjectured the existence of a "firewall effect" in which individuals who are infected with HIV, but remain in a state of low infectiousness, serve to prevent the virus from spreading. To evaluate this historical conjecture, we develop a new graph-theoretic measure that quantifies the extent to which Friedman's firewall hypothesis(FH)holds in a risk network. We compute this new measure across simulated trajectories of a stochastic discrete dynamical system that models a social network of 25,000 individuals engaging in risk acts over a period of 15 years. The model's parameters are based on analyses of data collected in prior studies of the real-world risk networks of people who inject drugs (PWID) in New York City. Analysis of system trajectories reveals the structural mechanisms by which individuals with mature HIV infections tend to partition the network into homogeneous clusters (with respect to infection status) and how uninfected clusters remain relatively stable (with respect to infection status) over long stretches of time. We confirm the spontaneous emergence of network firewalls in the system and reveal their structural role in the nonspreading of HIV.

Recent interest by physicists in social networks and disease transmission factors has prompted debate over the topology of degree distributions in sexual networks. Social network researchers have been critical of "scale-free" Barabasi-Albert approaches, and largely rejected the preferential attachment, "rich-get-richer" assumptions that underlie that model. Instead, research on sexual networks has pointed to the importance of homophily and local sexual norms in dictating degree distributions, and thus disease transmission thresholds. Injecting Drug User (IDU) network topologies may differ from the emerging models of sexual networks, however. Degree distribution analysis of a Brooklyn, NY, IDU network indicates a different topology than the spanning tree configurations discussed for sexual networks, instead featuring comparatively short cycles and high concurrency. Our findings suggest that IDU networks do in some ways conform to a "scale-free" topology, and thus may represent "reservoirs" of potential infection despite seemingly low transmission thresholds.