Received: 6 April 2020
Accepted: 18 December 2020
First Online: 8 January 2021
Ethics approval and consent to participate
: We obtained the written informed consent from every parent or guardian for participants under 16 years old and the approval from the ethics committee of the Affiliated Hospital of Qingdao University (QYFYW2LL25724).
: Not applicable.
: The authors declare that they have no competing interests.