Funding for this research was provided by:
Yunnan Provincial Foundation for Health Programmes (Grant no.  70.)
Guizhou Construction Platform for Talents Training (5735–31)
Received: 28 November 2019
Accepted: 6 February 2020
First Online: 19 February 2020
Ethics approval and consent to participate
: The Yunnan Provincial Center for Disease Control and Prevention ethics committee granted ethical approval for the study and used de-identified surveillance data. Written informed consent was obtained from each adult patient and 4-year-old patient’s mother for the study.
: Not applicable.
: The authors declare that they have no competing interest.