Funding for this research was provided by:
Ministry of Science and Technology of the People's Republic of China (2017YFD0500301, 2018ZX10715012, 2017ZX10201302-006-002)
National Natural Science Foundation of China (81872679)
Text and Data Mining valid from 2020-02-18
Received: 23 January 2019
Accepted: 11 February 2020
First Online: 18 February 2020
Ethics approval and consent to participate
: The study was approved by the Ethical Review Committee at Shanghai Municipal Center for Disease Control and Prevention. Since only anonymized secondary data were used, no informed consent was sought.
: Not applicable.
: The authors declare that they have no competing interests.