1. Usher Institute, University of Edinburgh, Edinburgh, United Kingdom;
2. Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, London, United Kingdom;
3. Division of Medicine, University College London, London, United Kingdom;
4. School of Medicine, University of St. Andrews, St. Andrews, United Kingdom; and
5. School of Public Health, University of the Witwatersrand, Johannesburg, South Africa