1. Division of Viral Diseases, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
2. Epidemic Intelligence Service, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
3. Maryland Department of Health Prevention and Health Promotion, Baltimore, Maryland, USA
4. Pennsylvania Department of Health, Harrisburg, Pennsylvania, USA
5. University Health Service, University of Michigan, Ann Arbor, Michigan, USA
6. Wisconsin Department of Health Services, Madison, Wisconsin, USA
7. University Health Center, University of Maryland, College Park, Maryland, USA
8. Virginia Department of Health, Richmond, Virginia, USA
9. Washtenaw County Health Department, Ypsilanti, Michigan, USA
10. University Health Services, University of Wisconsin, Madison, Wisconsin, USA
11. Henrico County Health Department, Virginia Department of Health, Richmond, Virginia, USA