Received: 19 September 2018
Accepted: 13 January 2019
First Online: 4 February 2019
Ethics approval and consent to participate
: This investigation was approved by the ethics committee of the Zhejiang Provincial Centre for Disease Control and Prevention (No. 2016020). Written informed consent for participation was obtained from all subjects or their legal guardians before conducting this survey. All data were supplied and analyzed in an anonymous format, with no personal identifying information provided to the researchers.
: Not applicable.
: The authors declare that they have no competing interests.
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