Emily S. Gurley, Amal K. Halder, Peter K. Streatfield, Hossain M. S. Sazzad, Tarique M. Nurul Huda, M. Jahangir Hossain, and Stephen P. Luby are with the International Centre for Diarrheal Diseases Research, Bangladesh (ICDDR,B), Dhaka, Bangladesh. Steven P. Luby is also with Centers for Disease Control and Prevention (CDC), Atlanta, GA.