Funding for this research was provided by:
Liaoning Provincial Science-Technology Department (2008225001)
Received: 8 December 2019
Accepted: 23 March 2020
First Online: 6 April 2020
Ethics approval and consent to participate
: This 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 this 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 a reason.
: Not applicable.
: The authors declare that they have no competing interests.