Funding for this research was provided by:
Key Technologies Research and Development Program (2018ZX10101002-004)
Text and Data Mining valid from 2019-07-12
Received: 25 March 2019
Accepted: 3 July 2019
First Online: 12 July 2019
Ethics approval and consent to participate
: The Ethics Review Board of the Shanxi Center for Disease Control and Prevention was consulted, since the project used surveillance date for a reportable disease of humans. So, ethics approval was not required because the data did not contain any personal or health information that could be connected back to the original identifiers.
: Not applicable.
: The authors declare that they have no competing interests.