Funding for this research was provided by:
National Natural Science Foundation of China (81671077, 81771180)
Natural Science Foundation of Beijing Municipality (Z170002)
Hainan Provincial Department of Health (2016YW20)
Natural Science Foundation of Beijing Municipality (15BJZ49)
Received: 5 November 2019
Accepted: 9 January 2020
First Online: 14 January 2020
Ethics approval and consent to participate
: The ethics committee of the Chinese PLA General Hospital approved this study. All respondents were informed of the purpose of the study. Written informed consent was obtained from all participants.
: Not applicable.
: The authors declare that they have no competing interests.