Received: 25 October 2017
Accepted: 28 June 2018
First Online: 20 July 2018
Ethics approval and consent to participate
: A parent and/or legal guardian of each participant signed a written informed consent document before enrollment and before any study procedure was performed. This study was approved by the Ethics Committee of the two hospitals (Ethics Committee of People’s Hospital of Zhongjiang County, and Ethics Committee of People’s Hospital of Chongqing Youyang County). No ethical problems were encountered in this study.
: Not applicable
: The authors declare that they have no competing interests.
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