Funding for this research was provided by:
Fund of Research and Development Program of Beijing Shunyi Health Planning Commissio (Wsjskyfzzx-z-04)
Received: 17 November 2018
Accepted: 13 September 2019
First Online: 22 October 2019
Ethics approval and consent to participate
: Approval for the study was obtained from the ethics committee of Beijing Shunyi Center for Disease Control and Prevention (Shunyi CDC). The verbal consent was obtained from one guardian (either father or mother) of each patient before enrollment. In an outbreak investigation situation, the ethics committee approved this procedure to conduct an investigation after obtaining verbal consent.
: Not applicable.
: The authors declare that they have no competing interests.