London School of Hygiene & Tropical Medicine - Department of Clinical Research, London School of Hygiene & Tropical Medicine - MRC Tropical Epidemiology Group (TEG), Biomedical Research and Training Institute, London School of Hygiene & Tropical Medicine, London School of Hygiene & Tropical Medicine - Department of Clinical Research, Clinical Research Department, London School of Hygiene and Tropical Medicine, Biomedical Research & Training Institute - The Health Research Unit Zimbabwe, Biomedical Research and Training Institute, London School of Hygiene & Tropical Medicine - MRC International Statistics & Epidemiology Group, MRC International Statistics and Epidemiology Group, Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, London School of Hygiene & Tropical Medicine - MRC International Statistics and Epidemiology Group, London School of Hygiene & Tropical Medicine - MRC International Statistics & Epidemiology Group, Biomedical Research and Training Institute, Ministry of Health and Child Care, Ministry of Health and Child Care, Ministry of Health and Child Care - Ministry of Health and Child Care AIDS and TB Unit and London School of Hygiene & Tropical Medicine - Department of Clinical Research