Received: 7 June 2018
Accepted: 7 May 2019
First Online: 17 May 2019
Ethics approval and consent to participate
: Our study was approved by Ethical Review Committee of NCNCD, China CDC. The actual name of the committee that approved the study is The Ethics Review Committee of the National Center for Chronic and Noncommunicable disease control and Prevention, Chinese Center for Disease Control and Prevention. We received verbal consent from all children’s legal guardians, which was approved by the ethics review board.
: Not applicable.
: The authors declare that they have no competing interests.
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