1. Departments of Laboratory Medicine and Biopharmaceutical Sciences, University of California, San Francisco, San Francisco, California
2. Division of Infectious Diseases, Department of Medicine, Columbia University College of Physicians and Surgeons, New York, New York
3. Division of Infectious Diseases, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
4. Statistical and Data Analysis Center, Harvard School of Public Health, Boston, Massachusetts