Funding for this research was provided by:
National Natural Science Foundation of China (81573204, 81773500)
Henan medical science and technology program (2018020510, 2018010029)
Text and Data Mining valid from 2019-06-24
Received: 27 February 2019
Accepted: 10 June 2019
First Online: 24 June 2019
Ethics approval and consent to participate
: The research was approved by the Ethical Committee of Henan Center for Disease Control and Prevention, and the committee’s reference number is (2016-KY-002-02). Not applicable for consent to participate.
: Not applicable.
: The authors declare that they have no competing interests.