1. Tibet Center for Disease Control and Prevention, Lhasa, Tibet
2. Shandong Provincial Chest Hospital, Jinan
3. Shigatse Center for Disease Control and Prevention, Shigatse, China
4. Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada
5. Weifang Medical University, Weifang
6. Shandong Center for Disease Control and Prevention, Academy of Preventive Medicine, Shandong University, Jinan, China