Aga Khan University - Department of Paediatrics and Child Health, Aga Khan University - Department of Paediatrics and Child Health, London School of Hygiene & Tropical Medicine - MRC Tropical Epidemiology Group (TEG), Aga Khan University - Department of Biological and Biomedical Sciences, Aga Khan University - Department of Community Health Sciences, Aga Khan University - Infectious Disease Research Laboratory, Ministry of Health Pakistan - Sindh AIDS Control Programme, Ministry of Health Pakistan - Sindh AIDS Control Programme, Ministry of Health Pakistan - Public Health Wing, Bridge Consultants Foundation, Pakistan, Ministry of Health Services - Pakistan - Nutrition Directorate, National AIDS Control Program, Pakistan, National AIDS Control Program, Pakistan, London School of Hygiene & Tropical Medicine - MRC Tropical Epidemiology Group (TEG), London School of Hygiene & Tropical Medicine - MRC Tropical Epidemiology Group (TEG), Aga Khan University - Section of Infectious Diseases and London School of Hygiene & Tropical Medicine - Department of Clinical Research