Funding for this research was provided by:
National Natural Science Foundation of China (81703279)
National Major Science and Technology Projects of China (2017ZX10201101)
Sichuan Science and Technology Program (2019YJ0148)
Received: 27 January 2020
Accepted: 27 May 2020
First Online: 23 June 2020
Ethics approval and consent to participate
: All subjects voluntarily participated in our study and signed informed consent forms before enrollment. For participants under 16 years old, written informed consent was obtained from their parents or guardians. The study protocol was approved by the Ethics Committee of the Sichuan Center for Disease Control and Prevention (201303), and the study was carried out following the Helsinki Declaration of 1964.
: Not application.
: The authors declare that they have no competing interests.