Text and Data Mining valid from 2020-04-09
Received: 9 December 2019
Accepted: 3 April 2020
First Online: 9 April 2020
Ethics approval and consent to participate
: The ethics committee of the Third Hospital of Hebei Medical University approved this research and waived the informed consent because this was a retrospective observational study, and all data were collected and analysed anonymously.
: Consent for publication was obtained from every individual whose data are included in this manuscript.
: The authors declare that they have no competing interests.