1. Wellcome Trust Tropical Centre, Liverpool School of Tropical Medicine, Liverpool, UK
2. Biomedical Research and Training Institute, Harare, Zimbabwe
3. University of Zimbabwe College of Health Sciences, Harare, Zimbabwe
4. Infectious Disease Epidemiology Unit, London School of Hygiene & Tropical Medicine, London, UK
5. Clinical Research Unit, London School of Hygiene & Tropical Medicine, London, UK