1. Department of Disease Control, LSHTM , Keppel Street, London WC1E 7HT, UK
2. Save the Children , Blantyre Field Office, Mandala, Private/Bag 254, Blantyre, Malawi
3. Save the Children , 501 Kings Highway East, Suite 400, Fairfield, CT 06825, USA
4. Department of Global Health and Development, LSHTM , 15-17 Tavistock Pl, London WC1H 9SH, UK
5. Department of Public Health, Environments and Society, LSHTM , 15-17 Tavistock Pl, London WC1H 9SH, UK