Funding for this research was provided by:
Medical and Health Technology Development Plan of Shandong Province (1)
Text and Data Mining valid from 2020-04-03
Received: 17 December 2019
Accepted: 25 March 2020
First Online: 3 April 2020
Ethics approval and consent to participate
: The study was approved by the Ethics Committee of the Yantai CDC.
: Not applicable.
: The authors declare that they have no competing interests.