Division of Epidemiology and Biostatistics, School of Public Health, University of California, Berkeley, Berkeley, California, United States of America.|Department of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, Georgia, United States of America.|Division of Viral Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.|Malawi-Liverpool-Wellcome Trust Clinical Research Programme, College of Medicine, University of Malawi, Blantyre, Malawi.|Malawi-Liverpool-Wellcome Trust Clinical Research Programme, College of Medicine, University of Malawi, Blantyre, Malawi.|Malawi-Liverpool-Wellcome Trust Clinical Research Programme, College of Medicine, University of Malawi, Blantyre, Malawi.|Department of Gastrointestinal Sciences, Christian Medical College, Vellore, Tamil Nadu, India.|Instituto Nacional de Ciences Médicas y Nutrición Salvador Zubirán, Mexico City, Mexico.|Instituto Nacional de Ciences Médicas y Nutrición Salvador Zubirán, Mexico City, Mexico.|Department of Gastrointestinal Sciences, Christian Medical College, Vellore, Tamil Nadu, India.|Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut, United States of America.