Funding for this research was provided by:
National Natural Science Foundation of China (71974165, 81473035)
Shenzhen Municipal Science and Technology Program (JCYJ20150630165236958)
Text and Data Mining valid from 2020-03-06
Received: 23 February 2019
Accepted: 26 February 2020
First Online: 6 March 2020
Ethics approval and consent to participate
: This study was reviewed and approved by the Medical Ethics Committee of the Guangdong CDC. Informed consent was waived by the Committee, as the data were collected for the purpose of routine public health surveillance activities. The data were anonymized before analysis.
: Not applicable.
: All authors declare that they have no competing interests.