1. Foodborne and Diarrheal Diseases Branch, Division of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia.
2. Epidemic Intelligence Service, Epidemiology Program Office, Centers for Disease Control and Prevention, Atlanta, Georgia.
3. Massachusetts Department of Health, Boston, Massachusetts.
4. Department of Microbiology, Immunology, and Pathology, Colorado State University, Fort Collins, Colorado.
5. Center for Food Safety, University of Georgia, Griffin, Georgia.
6. Biostatistics and Information Management Branch, Division of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia.