Article History
Received: 14 May 2020
Accepted: 29 December 2020
First Online: 13 January 2021
Ethics approval and consent to participate
: This study was reviewed and approved by the ethics committees of the National Center for AIDS/STD Control and Prevention, Chinese Center for Disease Control and Prevention(X190311560). Informed consent is not applicable to this study because only data that are anonymous in the CRS were used.
: Not applicable.
: The authors declare that they have no competing interests.