Received: 19 September 2019
Accepted: 16 December 2019
First Online: 21 December 2019
Ethics approval and consent to participate
: The institutional ethics committee of the First Hospital of Jilin University (ChiCTR1800020196) approved the study. The parents or guardians of the eligible children provided written informed consent. An information sheet was provided for the parents or guardians of all participants.
: Not applicable.
: The authors declare that they have no competing interests.