1. Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
2. Division of Viral Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
3. Departments of Medicine and Pediatrics, Emory University School of Medicine, Atlanta, Georgia, USA
4. Georgia Emerging Infections Program, Atlanta Veterans Affairs Medical Center, Atlanta, Georgia, USA
5. Minnesota Department of Health, St. Paul, Minnesota, USA
6. California Emerging Infections Program, Oakland, California, USA
7. Oregon Public Health Division, Portland, Oregon