1. Center for Epidemiology and Animal Health, Animal and Plant Health Inspection Service, U.S. Department of Agriculture, Fort Collins, Colorado.
2. Bacterial Epidemiology and Antimicrobial Resistance Unit, Agricultural Research Service, U.S. Department of Agriculture, Athens, Georgia.
3. National Veterinary Services Laboratories, Animal and Plant Health Inspection Service, U.S. Department of Agriculture, Ames, Iowa.