1. Department of Population Health, London School of Hygiene & Tropical Medicine, London, UK
2. Department of Infectious Disease Epidemiology, Imperial College London, London, UK
3. African Population and Health Research Centre, P.O. Box 10787-00100, Nairobi, Kenya
4. KEMRI/CDC Center for Global Health Research (CGHR), P.O. Box 1578, Kisumu, Kenya
5. Public Health Consultant, P.O. Box 42614-00100, Nairobi, Kenya