Funding for this research was provided by:
National Natural Science Foundation of China (11501339)
Text and Data Mining valid from 2018-05-18
Received: 16 October 2017
Accepted: 27 April 2018
First Online: 18 May 2018
Ethics approval and consent to participate
: The study was approved by the Medical Research Ethics Committee of the University of Queensland (No. 2016001608) and Beijing Institute of Disease Control and Prevention. Patient confidentiality was ensured throughout the analysis of the data through data de-identification and aggregation of data records to the county-level.
: The authors have declared that no competing interests exist.