1. Department of Epidemiology, George Washington University Milken Institute School of Public Health, Washington, DC, USA
2. Howard University Department of Pediatrics and Child Health, Washington, DC, USA
3. Division of Infectious Diseases, George Washington University School of Medicine and Health Sciences, Washington, DC, USA
4. Infectious Diseases Section, DC Veterans Administration Medical Center, Washington, DC, USA
5. Mid-Atlantic Permanente Research Institute, Washington, DC, USA