1 Saw Swee Hock School of Public Health, National University of Singapore, Singapore; Ministry of Health, Singapore 169854. Electronic address: vernonljm@hotmail.com.
2 Ministry of Health, Singapore 169854.
3 London Universidad del Desarrollo, Saniago, Chile.
4 London School of Hygiene & Tropical Medicine, London, UK.
5 London School of Hygiene & Tropical Medicine, London, UK; Heidelberg Institute of Global Health, University of Heidelberg, Heidelberg, Germany.