Received: 6 March 2018
Accepted: 28 January 2019
First Online: 4 February 2019
Ethics approval and consent to participate
: This study was approved by the Research Ethics Committee of Kowloon Central/Kowloon East Cluster, Hong Kong, and patient consent was not required because this was a retrospective study. Furthermore, all the participants were anonymous.
: Not applicable.
: The authors declare that they have no competing interests.
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