1. University of Maryland, Division of Infectious Diseases, Institute of Human Virology, 725 West Lombard Street, Baltimore, MD 21201, USA; Baltimore City Health Department, Baltimore, MD, USA
2. Bloomberg School of Public Health, Department of Epidemiology, Baltimore, MD, USA
3. Johns Hopkins University, School of Medicine, Department of Medicine, Baltimore, MD, USA
4. Baltimore City Health Department, Baltimore, MD, USA; Johns Hopkins University, School of Medicine, Department of Medicine, Baltimore, MD, USA