Received: 15 February 2019
Accepted: 21 October 2019
First Online: 4 November 2019
Ethics approval and consent to participate
: This study was approved by the Joint Chinese University of Hong Kong-New Territories East Cluster Clinical Research Ethics Committee: Ref No.2016.031-T. Written consent was obtained from the mothers of all participants of the study.
: Not applicable.
: The authors declare that they have no competing interests.