1. Division of Pulmonary, Sleep and Critical Care Medicine, Department of Internal Medicine, Korea University Ansan Hospital, Korea University College of Medicine, Ansan, Korea.
2. Korea Institute of Tuberculosis, Cheongju, Korea.
3. Medical Science Research Center, Korea University Ansan Hospital, Korea University College of Medicine, Ansan, Korea.
4. Settlement Support Center for North Korean Refugees (Hanawon), Hwacheon, Korea.