1. Saw Swee Hock School of Public Health, National University of Singapore and National University Health System, 1E Kent Ridge Rd, Singapore 117549
2. Department of Disease Control, London School of Hygiene & Tropical Medicine, Keppel St, Bloomsbury, London WC1E 7HT, UK
3. Heidelberg Institute of Global Health, University of Heidelberg, Im Neuenheimer Feld 365, R. 004, 69120 Heidelberg, Germany