Received: 20 August 2019
Accepted: 11 November 2019
First Online: 5 December 2019
Ethics approval and consent to participate
: This study has been approved by the Kowloon West Cluster Research Ethics Committee (reference number KW/EX-16-155[103–08]). Written informed consent was obtained from all participants prior to collecting oral rinse samples.
: Not applicable.
: The authors declare that they have no competing interests.