Funding for this research was provided by:
Chinese Association of Preventive Medicine (20180103)
Shanghai Health Commission (201840334)
Text and Data Mining valid from 2020-03-19
Received: 16 July 2019
Accepted: 21 February 2020
First Online: 19 March 2020
Ethics approval and consent to participate
: The protocol for this research was approved by the Ethical Review Board of the Shanghai Municipal Center for Disease Control and Prevention (SCDC). Informed consent was exempted because it was limited to analysis of previously de-identified data collected for medical and public health surveillance purposes.
: Not applicable.
: The authors declare that they have no competing interests.