title: Modified social ecological model: a tool to guide the assessment of the risks and risk contexts of HIV epidemics.
abstract: BACKGROUND
  Social and structural factors are now well accepted as determinants of HIV vulnerabilities. These factors are representative of social, economic, organizational and political inequities. Associated with an improved understanding of multiple levels of HIV risk has been the recognition of the need to implement multi-level HIV prevention strategies. Prevention sciences research and programming aiming to decrease HIV incidence requires epidemiologic studies to collect data on multiple levels of risk to inform combination HIV prevention packages.
  
  
  CONCLUSIONS
  Proximal individual-level risks, such as sharing injection devices and unprotected penile-vaginal or penile-anal sex, are necessary in mediating HIV acquisition and transmission. However, higher order social and structural-level risks can facilitate or reduce HIV transmission on population levels. Data characterizing these risks is often far more actionable than characterizing individual-level risks. We propose a modified social ecological model (MSEM) to help visualize multi-level domains of HIV infection risks and guide the development of epidemiologic HIV studies. Such a model may inform research in epidemiology and prevention sciences, particularly for key populations including men who have sex with men (MSM), people who inject drugs (PID), and sex workers. The MSEM builds on existing frameworks by examining multi-level risk contexts for HIV infection and situating individual HIV infection risks within wider network, community, and public policy contexts as well as epidemic stage. The utility of the MSEM is demonstrated with case studies of HIV risk among PID and MSM.
  
  
  CONCLUSIONS
  The MSEM is a flexible model for guiding epidemiologic studies among key populations at risk for HIV in diverse sociocultural contexts. Successful HIV prevention strategies for key populations require effective integration of evidence-based biomedical, behavioral, and structural interventions. While the focus of epidemiologic studies has traditionally been on describing individual-level risk factors, the future necessitates comprehensive epidemiologic data characterizing multiple levels of HIV risk.
authors.affiliation: Center for Public Health and Human Rights, Johns Hopkins Bloomberg School of Public Health, Johns Hopkins University, 615 N, Wolfe Street, Baltimore, MD 21205, USA. sbaral@jhsph.edu
authors.forename: Stefan
authors.initials: S
authors.lastname: Baral
authors.forename: Carmen H
authors.initials: CH
authors.lastname: Logie
authors.forename: Ashley
authors.initials: A
authors.lastname: Grosso
authors.forename: Andrea L
authors.initials: AL
authors.lastname: Wirtz
authors.forename: Chris
authors.initials: C
authors.lastname: Beyrer
mesh_terms: D058872:Epidemics / Q000517:prevention & control; D005260:Female; D015658:HIV Infections / Q000453:epidemiology* / Q000517:prevention & control / Q000635:transmission; D006801:Humans; D008297:Male; D015233:Models, Statistical; D011640:Public Policy; D018570:Risk Assessment; D012307:Risk Factors; D012309:Risk-Taking; D012725:Sexual Behavior; D012944:Social Support