Funding for this research was provided by:
Foundation of Shanghai Municipal Commission of Health and Family Planning (15GWZK1001)
Shanghai Xuhui District Medical Peak Plateau Discipline Project (SHXH201723)
Received: 17 February 2019
Accepted: 4 December 2019
First Online: 19 December 2019
Ethics approval and consent to participate
: This study received ethical clearance from Ethics Committee of Xuhui District Center for Disease Control and Prevention. Consent (assent for students below 18 years, after written consent from the parents) was asked directly from the participants. All participants in this research gave written informed consent.
: Not applicable.
: The authors declare that they have no competing interests.