1. International Centre for Diarrhoeal Disease Research; Bangladesh GPO Box 128 Dhaka 1000 Bangladesh
2. Department of Microbiology; University of Dhaka; Dhaka 1000 Bangladesh
3. Department of Medicine, Division of Infectious Diseases and Geographic Medicine, and Department of Microbiology and Immunology; Stanford University School of Medicine; Stanford CA 94305 U.S.A.