1. International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b), Dhaka, Bangladesh;
2. Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland;
3. Division of Epidemiology and Biostatistics, School of Public Health, University of California Berkeley, Berkeley, California;
4. School of Public Health and Health Professions, University at Buffalo, Buffalo, New York;
5. Division of Infectious Diseases and Geographic Medicine, Stanford University, Stanford, California