Funding for this research was provided by:
National Health and Family Planning Commission of the People's Republic of China (201502025)
Key Medical Specialty Development Plan of Beijing Hospital Administration (ZYLX201829)
Received: 4 October 2018
Accepted: 5 June 2019
First Online: 18 June 2019
Ethics approval and consent to participate
: This study was approved by the Ethics Committee of the Capital Institute of Pediatrics (SHERLL-2013072). All parents of the recruited children gave informed consent.
: The authors declare that they have no competing interests.