Funding for this research was provided by:
Nanjing Municipal Science and Technique Development Foundation (201715058)
Nanjing Medical Science and Technique Development Foundation (ZKX16052)
Received: 3 May 2020
Accepted: 1 October 2020
First Online: 12 October 2020
Ethics approval and consent to participate
: Written informed consent was obtained from both schools and parents/guardians prior to the on-site survey. Academic and Ethics Committee of Nanjing Municipal Center for Disease Control and Prevention, China, reviewed and approved this study.
: The authors declare that they have no competing interests.