Funding for this research was provided by:
Department of Science and Technology of Liaoning Province (2005225012)
Received: 7 February 2020
Accepted: 5 October 2020
First Online: 9 November 2020
Ethics approval and consent to participate
: The study was conducted in accordance with the Declaration of Helsinki on ethical principles for medical research involving human subjects. The ethics committee of Liaoning Provincial Center for Disease Control and Prevention (LNCDCP) approved the study. All subjects gave written informed consent after the study objectives were explained, and all subjects were free to withdraw at any time without giving any reason.
: Not applicable.
: The authors have declared that no competing interests exist.