Conflicts of interest
The authors have no conflicts of interest.
Authors’ contributions: Hong-Li Liu is first author and Hong-Bo
Qi obtained the funding. Lan Zhang and Hong-Li Liu designed the study.
Hong-Li Liu, Shuai Huang and Jun-Nan Li collected the data. Hong-Li Liu
and Lan Zhang analyzed the data. Hong-Li Liu drafted the manuscript. Lan
Zhang contributed to the interpretation of the results and critical
revision of the manuscript for important intellectual content and
approved the final version of the manuscript. All authors have read and
approved the final manuscript. Lan Zhang is the study guarantor.