1. Division of Infectious Diseases, Massachusetts General Hospital, Boston, Massachusetts;
2. International Center for Diarrheal Disease Research, Bangladesh (icddr,b), Dhaka, Bangladesh;
3. Department of Medicine, Harvard Medical School, Boston, Massachusetts;
4. Department of Pediatrics, Harvard Medical School, Boston, Massachusetts;
5. Department of Microbiology, Harvard Medical School, Boston, Massachusetts;
6. Department of Immunology and Infectious Disease, Harvard School of Public Health, Boston, Massachusetts;