Received: 7 April 2019
Accepted: 14 May 2019
First Online: 23 May 2019
Ethics approval and consent to participate
: Permission to conduct this study was obtained from the Ethics Committee of the First Affiliated Hospital of Guangzhou Medical College (No. 2012-51). Informed consent was obtained from all individual participants included in the study. All procedures involving human participants were in accordance with the ethical standards of the committee.
: Not applicable.
: The authors declare that they have no competing interests.