1. Pacific Institute for Research and Evaluation, Calverton, Maryland, USA
2. Department of Behavioral Medicine & Psychiatry, West Virginia University, Morgantown, West Virginia, USA
3. Department of Epidemiology, West Virginia University, Morgantown, West Virginia, USA
4. Fresno Needle Exchange Program, Fresno, California, USA
5. Department of Anthropology, University of California, Riverside, Riverside, California, USA