1. Kenya Medical Research Institute, Wellcome Trust Research Programme, Nairobi, Kenya
2. Department of Paediatrics and Child Health, College of Health Sciences, University of Nairobi, P.O. Box 19676–00202, Nairobi, Kenya
3. Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, Oxford University, Old Road campus, Roosevelt Drive, Headington, Oxford OX3 7FZ, UK