1. Division of Infectious Diseases, Nemours/Alfred I. duPont Hospital for Children, Wilmington, Delaware;
2. Department of Pediatrics, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania;
3. Center for Pediatric Clinical Effectiveness and
4. Department of Biostatistics and Epidemiology,
5. Center for Clinical Epidemiology and Biostatistics, and
6. Division of Infectious Diseases, Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania; and
7. Department of Pediatrics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania