1. Center for AIDS Prevention Studies, Department of Medicine, University of California, San Francisco, CA 94143, USA
2. Family & Community Medicine, Department of Medicine, University of California, San Francisco, CA 94143, USA
3. Centre on Drug Policy Evaluation, St. Michael’s Hospital, Toronto, ON M5B 1W8, Canada
4. Division of Infectious Diseases & Global Public Health, UC San Diego School of Medicine, University of California, San Diego, CA 92093, USA
5. San Francisco AIDS Foundation, San Francisco, CA 94103, USA