Received: 13 February 2020
Accepted: 27 May 2020
First Online: 9 June 2020
Ethics approval and consent to participate
: The study was performed with the approval of the Ethics Committee of the Affiliated University of Qingdao University (no: 20190113). The protocol was designed and the study was conducted according to the principles of the Declaration of Helsinki (1964). Written informed consent was obtained from all participants. Consent was obtained from a parent or guardian on behalf of any participants under the age of 16 years.
: Not applicable.
: The authors declare that they have no competing interests.