Funding for this research was provided by:
Ningbo Health Branding Subject Fund (ppxk2018-10)
the Science and Technology Planning Project of Ningbo (2018A610407)
The Public Welfare Technology Application Research Funding Projects of Zhejiang Province (LGF20H260006)
Received: 9 October 2020
Accepted: 3 June 2021
First Online: 10 June 2021
: The protocol for this research was approved by the Research Ethics Review Board of Ningbo Municipal Center for Disease Prevention and Control(No.202013). Informed consent was exempted because it was limited to analysis of previously de-identified data collected for public health surveillance purposes.
: Not applicable.
: The authors declare that they have no competing interests.