Text and Data Mining valid from 2020-04-19
Received: 13 May 2019
Accepted: 30 March 2020
First Online: 19 April 2020
Ethics approval and consent to participate
: Ethical approval is not required for conducting this type of survey in China, because the data used in this paper were medical record data. This study did no direct contact with human subjects (reference file # Science and Education Department of Ministry of Health  17# ExternalRef removed). All of the information from institutions or study-related persons was anonymized and de-identified prior to analysis.
: Not applicable.
: The authors declare that they have no competing interests.