A Multilevel Ecological Model of HIV Risk for People Who Are Homeless or Unstably Housed and Who Use Drugs in the Urban United States.

Elevated HIV prevalence has been observed among urban U.S. individuals who use drugs and who lack stable housing. This article synthesizes extant research on this population and situates it in a multilevel, ecologically based model of HIV risk. Based on a multidisciplinary review of the literature, the model applies social-ecological theory on human development to identify factors shaping the HIV risk context for individuals who use drugs and who are unstably housed at global, societal, neighborhood, household, and individual levels of influence. At the global level, the model includes neoliberal ideologies contributing to the social inequalities that frame the HIV epidemic. U.S. housing and drug policy, including urban renewal, HOPE VI, and the War on Drugs, is the focus of the societal level. At the neighborhood level, mechanisms of the built environment and psychosocial mechanisms are explored for their salience to HIV risk. Research on the association between housing instability and HIV risk is reviewed at the household level. At the last level, relevant individual differences in biology, psychology, and cognition are discussed. Modeling risk at multiple levels of the environment underscores the need to expand the focus of research, treatment, and prevention interventions for HIV/AIDS and addictions beyond individuals and their risk behaviors to address facets of structural violence and incorporate the broader social, political, and economic contexts of risk and health.