1. Department of Respiratory Medicine, The Second Hospital of Anhui Medical University, Hefei, Anhui 230022, P.R. China
2. Department of Respiratory Medicine, The Second People's Hospital of Hefei, Hefei, Anhui 230022, P.R. China
3. Department of Respiratory Medicine, The First Hospital of Anhui Medical University, Hefei, Anhui 230022, P.R. China
4. The Teaching Center for Preventive Medicine, School of Public Health, Anhui Medical University, Hefei, Anhui 230022, P.R. China