1. Division of Infectious Diseases and Global Public Health, Department of Medicine, University of California San Diego, La Jolla, California
2. Biostatistics Research Center, Department of Family Medicine and Public Health, University of California San Diego, La Jolla, California
3. VA San Diego Healthcare System, San Diego, California
4. Division of Infectious Diseases, Denver Health Medical Center, Denver, Colorado
5. School of Social and Community Medicine, University of Bristol, Bristol, UK