1. Faculty of Public Health and Policy, London School of Hygiene & Tropical Medicine, 15-17 Tavistock Place, London WC1H 9SH, UK
2. Epidemiology and Demography Department, KEMRI Wellcome Trust Research Programme, CGMRC, PO Box 230-80108 Kilifi, Kenya
3. Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, Keppel Street, London WC1E 7HT, UK
4. Health Systems and Research Ethics Department, KEMRI Wellcome Trust Research Programme, CGMRC, PO Box 230-80108 Kilifi, Kenya