1. Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, MD
2. Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD
3. Office of Epidemiology, Division of Disease Prevention, Virginia Department of Health, Richmond, VA
4. Department of Epidemiology and Community Health, School of Medicine, Virginia Commonwealth University, Richmond, VA
5. Baltimore City Health Department, Baltimore, MD
6. Division of Infectious Disease, Johns Hopkins University School of Medicine, Baltimore, MD