1. Divisions of General Pediatrics and Infectious Diseases, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania
2. Child Health Corporation of America, Shawnee Mission, Kansas
3. Departments of Internal Medicine and Pediatrics, Carilion Clinic Children's Hospital, Roanoke, Virginia
4. Departments of Pediatrics and Epidemiology and Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania