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Article History

Received: 8 October 2017

Accepted: 23 May 2018

First Online: 31 May 2018

Ethics approval and consent to participate

: This study was reviewed and approved by the Ethics Committee of Beijing Children’s Hospital Affiliated to Capital Medical University (2017-k-83). Informed consent was waived because this was a retrospectively study. We obtained patient data from the Medical Records and Statistics Room. We analysed the data anonymously.

: The authors declare that they have no competing interests.

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