1 Department of Clinical Sciences, Liverpool School of Tropical Medicine, Liverpool L3 5QA, UK. Electronic address: penelope.phillips-howard@lstmed.ac.uk.
2 Department of Environmental Health and Engineering, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA.
3 MRC Tropical Epidemiology Group, London School of Hygiene & Tropical Medicine, London, UK.
4 WoMena Uganda, Kampala, Uganda.
5 Department of Sociomedical Sciences, Mailman School of Public Health, Columbia University, New York, NY, USA.