1. KEMRI-Wellcome Trust Research Programme , P.O. Box 43640-00100, Nairobi, Kenya
2. Ministry of Health, Kilifi County Government , P.O. Box 519-80108, Kilifi, Kenya
3. Centre for Tropical Medicine and Global Health, Nuffield Department of Clinical Medicine, University of Oxford , New Richards Building, Old Road Campus, Roosevelt Drive, OX3 7LG, Oxford, UK