1. Enteric Diseases Department, Naval Medical Research Center, Silver Spring, Maryland 209101;
2. Infection Discovery Astra Zeneca, Cambridge, Massachusetts 021392;
3. Food and Drug Administration, Beltsville, Maryland 207083; and
4. Laboratory of Enteric and Sexually Transmitted Diseases, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland 208924