1. Water and Environment Activity, Division of Parasitic Diseases, Centers for Disease Control and Prevention, 4770 Buford Highway, N.E., Mailstop F22, Atlanta, GA 30341-3724, USA
2. Foodborne Diseases Active Surveillance Network (FoodNet), Foodborne and Diarrheal Diseases Branch, Centers for Disease Control and Prevention, 1600 Clifton Road, Mailstop D63, Atlanta, GA 30333, USA