Pieter Baker and Javier A. Cepeda are with the Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD. Leo Beletsky is with the Bouvé College of Health Sciences and School of Law, Northeastern University, Boston, MA. Richard Garfein and Steffanie A. Strathdee are with the Department of Medicine, University of California, San Diego. Eileen Pitpitan and Eyal Oren are with the Graduate School of Public Health, San Diego State University, San Diego, CA.