1. Perelman School of Medicine, University of Pennsylvania, Philadelphia
2. Division of Infectious Diseases and Center for Pediatric Clinical Effectiveness Research, Children’s Hospital of Philadelphia, Pennsylvania
3. Lovelace Respiratory Research Institute, Albuquerque, New Mexico
4. Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania, Philadelphia
5. Department of Pediatrics, University of Pennsylvania, Philadelphia
6. Department of Biostatistics and Epidemiology, University of Pennsylvania, Philadelphia