Received: 12 July 2018
Accepted: 15 October 2019
First Online: 26 November 2019
Ethics approval and consent to participate
: Outbreak investigation was a part of CDC’s routine responsibilities and formal ethics approval was not required according to the law of the People’s Republic of China on prevention and control of infectious disease (revised in 2013). We obtained written informed consents from parents of patients during the outbreak investigation.
: Not applicable
: The authors declare that they have no competing interests.