Funding for this research was provided by:
National Basic Research Program of China (973 Program) (2012CB955500-95502)
Ministry of Science and Technology of the People's Republic of China (2017FY101202)
Text and Data Mining valid from 2019-11-12
Received: 3 July 2019
Accepted: 24 October 2019
First Online: 12 November 2019
Ethics approval and consent to participate
: All the cases involved in this study were obtained from China National Notifiable Disease Surveillance System (NDSS) without their names and the work was approved by the Ethical Review Committee (ERC) of School of Public Health in Shandong University (20120501), and consent from the participants’ parent or guardian was exempted. Permissions from the ERC of School of Public Health in Shandong University were required to access the raw data because the data involved patient privacy.
: Not applicable.
: The authors declare that they have no competing interests.