About the Authors
Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, United States of America
Headquarters Medical Corps, Singapore Armed Forces, Singapore, Singapore
The authors have declared that no competing interests exist.
Performed the experiments: BMA. Analyzed the data: BMA. Wrote the paper: BMA YYN DATC. Conceived the study: DATC YYN. Designed the analysis: BMA DATC.