Funding for this research was provided by:
Ministry of Environment and Water Resources, Singapore
Received: 9 August 2018
Accepted: 27 December 2018
First Online: 8 January 2019
Ethics approval and consent to participate
: The permission to use these data was approved by the Ministry of Health, Singapore and National Environment Agency, Singapore.
: Not applicable.
: The authors declare that they have no competing interests.
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