1 London School of Hygiene & Tropical Medicine, Department of Public Health, Environments and Society, 15-17 Tavistock Place, London WC1H 9SH, United Kingdom. Electronic address: Magdalena.harris@lshtm.ac.uk.
2 London School of Hygiene & Tropical Medicine, Department of Public Health, Environments and Society, 15-17 Tavistock Place, London WC1H 9SH, United Kingdom.