1. Department of Pediatrics, University of Colorado Denver School of Medicine, Anschutz Medical Campus , Aurora, Colorado , USA
2. Department of Medicine, University of Colorado Denver School of Medicine, Anschutz Medical Campus , Aurora, Colorado , USA
3. Department of Pathology, University of Colorado Denver School of Medicine, Anschutz Medical Campus , Aurora, Colorado , USA
4. Viral Vaccine Preventable Diseases Branch, Division of Viral Diseases, Centers for Disease Control and Prevention , Atlanta, Georgia , USA