Article History
Received: 31 July 2020
Accepted: 9 December 2020
First Online: 5 January 2021
Ethics approval and consent to participate
: This retrospective study without intervention was approved by Peking Union Medical College Hospital Ethical Committee. A written informed consent was obtained from a parent or guardian for participants under 16 years old when admitted into ward about medical records for scientific use.
: Not Applicable.
: NA