Funding for this research was provided by:
National Natural Science Foundation of China (81372982)
Text and Data Mining valid from 2019-06-10
Received: 25 February 2019
Accepted: 10 May 2019
First Online: 10 June 2019
Ethics approval and consent to participate
: The study was approved by the Ethics Committee of the West China School of Public Health (No. 4 West China Teaching Hospital) of Sichuan University at March 3, 2012. All participants’ guardians provided written informed consent to participate in the study.
: Not applicable.
: The authors declare that they have no competing interests.
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