Nutrition and Clinical Services Division (NCSD), International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b), Dhaka, Bangladesh. Department of Gastroenterology, Dhaka Medical College and Hospital, Dhaka, Bangladesh. Apollo Hospital, Dhaka, Bangladesh. Department of Paediatric Gastroenterology, Hepatology & Nutrition, Dhaka Shishu Hospital, Dhaka, Bangladesh. Department of Paediatric Gastroenterology & Nutrition, Bangabandhu Sheikh Mujib Medical University (BSMMU), Dhaka, Bangladesh. Division of Infectious Diseases and International Health, University of Virginia, Charlottesville, Virginia, USA. Center for Genome Sciences and Systems Biology, Washington University, St Louis, Missouri, USA. Center for Gut Microbiome and Nutrition Research, Washington University, St. Louis, Missouri, USA.