Funding for this research was provided by:
Young Medical Talents Program of Jiangsu Province of China (QNRC2016230)
Received: 16 April 2019
Accepted: 30 June 2019
First Online: 19 July 2019
Ethics approval and consent to participate
: The study protocol was approved by the ethics committees of Suzhou Centers for Disease Control and Prevention in accordance with the ethical guidelines of the 1975 Declaration of Helsinki. Written informed consents were obtained from the parents of children after declaring the objectives of the present study.
: Not applicable.
: The authors declare that they have no competing interests.