1 Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA; Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, USA. Electronic address: vetter@chop.edu.
2 Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA.
3 Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, USA.
4 Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA; Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, USA.
5 CARES Surveillance Group.
6 CARES Surveillance Group; Emory University, Woodruff Health Sciences Center, Atlanta, Georgia, USA; Rollins School of Public Health, Atlanta, Georgia, USA.
7 Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA; Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, USA; Center for Pediatric Clinical Effectiveness, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA.