Saw Swee Hock School of Public Health, National University of Singapore and National University Health System, Singapore, Singapore.|Interdisciplinary Research Group in Infectious Diseases, Singapore-MIT Alliance for Research & Technology, Singapore, Singapore and.|Saw Swee Hock School of Public Health, National University of Singapore and National University Health System, Singapore, Singapore.|Saw Swee Hock School of Public Health, National University of Singapore and National University Health System, Singapore, Singapore, National University of Singapore Environment Research Institute, Singapore, Singapore.|Saw Swee Hock School of Public Health, National University of Singapore and National University Health System, Singapore, Singapore.|Saw Swee Hock School of Public Health, National University of Singapore and National University Health System, Singapore, Singapore.