1. Epidemic Intelligence Service, Centers for Disease Control and Prevention , Atlanta, Georgia , USA
2. Division of Healthcare Quality Promotion, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention , Atlanta, Georgia , USA
3. Division of Infectious Diseases, Department of Medicine, Washington University School of Medicine , St Louis, Missouri , USA
4. Division of Infectious Diseases, Department of Pediatrics, School of Medicine, University of Utah , Salt Lake City, Utah , USA
5. Division of Public Health Sciences, Department of Surgery, Washington University School of Medicine , St Louis, Missouri , USA