Funding for this research was provided by:
Guangdong Medical Research Foundation (A2018136)
Annual special research of the health industry, China, 2012
Received: 6 December 2018
Accepted: 2 April 2019
First Online: 14 May 2019
: Authors’ information has been listed in the first page of the manuscript.
: This study was conducted according to the guidelines laid down in the Declaration of Helsinki and all procedures involving human subjects/patients were approved by the Sun Yat-sen University ethic committee. Written informed consent was obtained from all parents of children.
: Not applicable.
: The authors declare that they have no competing interests.
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