Received: 16 August 2017
Accepted: 9 March 2018
First Online: 6 April 2018
Ethics approval and consent to participate
: The study was approved by the ethical review committee of the Affiliated Hospital of Qingdao University and all the other participating centers, and each procedure during this study was carried out according to the principles established in the Helsinki Declaration. At enrolment time, the parents of all eligible children who met the inclusion criteria signed the informed consent form.
: Consent to publish has been obtained from.the parents of all children. There is a declaration on ICF that all research data will be used for scientific research and publication.
: The authors declare that they have no competing interests.
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