1. Division of Infectious Disease Epidemiology, Pennsylvania Department of Health, Harrisburg, Pennsylvania.
2. Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania.
3. Pennsylvania Department of Health Bureau of Laboratories, Exton, Pennsylvania.
4. Pennsylvania Department of Agriculture, Harrisburg, Pennsylvania.
5. Centers for Disease Control and Prevention, Atlanta, Georgia.
6. National Institutes of Health, Bethesda, Maryland.
7. Atlanta Research and Education Foundation, Atlanta, Georgia.
8. U.S. Food and Drug Administration, Center for Veterinary Medicine, Laurel, Maryland.