1. 1Enteric Diseases Epidemiology Branch, Centers for Disease Control and Prevention, 1600 Clifton Road N.E., MS A-38, Atlanta, Georgia 30333
2. 2Center for Food Safety and Department of Food Science and Technology, University of Georgia, 1109 Experiment Street, Griffin, Georgia 30223-1797
3. 3Division of Foodborne, Bacterial and Mycotic Diseases, Centers for Disease Control and Prevention, 1600 Clifton Road N.E., MS C-09, Atlanta, Georgia 30333, USA