1. Division of Foodborne, Waterborne and Environmental Diseases, U.S. Centers for Disease Control and Prevention, Atlanta, Georgia;
2. Center for Surveillance, Epidemiology, and Laboratory Services, U.S. Centers for Disease Control and Prevention, Atlanta, Georgia;
3. Department of Experimental Pathology, Immunology and Microbiology, Faculty of Medicine, American University of Beirut, Beirut, Lebanon