1 State Key Laboratory of Respiratory Disease, National Clinical Research Center for Respiratory Disease, First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China.
2 Department of Epidemiology, School of Public Health and Tropical Medicine, Southern Medical University, Guangdong, China.
3 State Key Laboratory of Respiratory Disease, National Clinical Research Center for Respiratory Disease, First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China. Electronic address: jpzhenggy@163.com.