1. A complex systems approach to evaluate HIV prevention in metropolitan areas: Preliminary implications for combination intervention strategies Brandon DL Marshall, PhD Department of Epidemiology Brown University Magdalena M Paczkowski & Sandro Galea, Columbia University Lars Seemann, University of Houston Barbara Tempalski, Enrique Pouget, & Samuel R Friedman, NDRI Inc.

2. Introduction & Conceptual Framework The conceptual framework represents causal effects between two phenomena – agent characteristics, behaviors & interventions, outputs – in the agent-based model (ABM):

3. Transmission through an ABM risk network: HM HF WSW MSM IDU NIDU NDU Legend:

4. Estimated HIV Prevalence/Incidence among IDU

5. Conclusions The ABM closely approximated HIV prevalence and incidence among drug users in New York City, 1992-2002. Future work will identify optimal combinations of HIV prevention interventions for drug-using populations. Although not without challenges, complex systems approaches have the potential to inform real world policy scenarios, including combined HIV prevention strategies. Additional results will be presented in oral abstract late breaker session C, Friday July 27 th at 11:00am in Session Room 6. This project is funded in part by a 2012 developmental grant from the Lifespan/Tufts/Brown Center for AIDS Research (P30AI042853) and by the National Institutes of Health (R01-DA013336) as part of the Community Vulnerability and Responses to Drug- User Related HIV/AIDS (CVAR) study. Brandon Marshall was supported by a Postdoctoral Fellowship from the Canadian Institutes of Health Research. Lars Seemann is supported by the National Science Foundation (Award Number 0840889).