1 Department of Primary Care and Public Health, Brighton and Sussex Medical School, Falmer, BN1 9PH, UK; School of Life Sciences, University of Sussex, Falmer, UK. Electronic address: j.middleton@bsms.ac.uk.
2 Department of Primary Care and Public Health, Brighton and Sussex Medical School, Falmer, BN1 9PH, UK; Public Health England South East, Horsham, UK.
3 Department of Primary Care and Public Health, Brighton and Sussex Medical School, Falmer, BN1 9PH, UK.
4 Faculty of Medicine and Global Health Research Institute, University of Southampton, Southampton, UK.
5 Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK.