Department of Internal Medicine, Chung-Ang University Hospital, Seoul, Republic of Korea. Department of Pulmonology and Critical Care Medicine, Kyung Hee University Hospital, Seoul, Republic of Korea. Department of Internal Medicine, College of Medicine, Seoul St Mary's Hospital, The Catholic University of Korea, Seoul, Republic of Korea. Department of Internal Medicine, College of Medicine, Korea University Hospital, Seoul, Republic of Korea. Department of Internal Medicine, Soonchunhyang University Bucheon Hospital, Bucheon, Republic of Korea. Department of Internal Medicine, Hallym University Kangnam Hospital, Seoul, Republic of Korea. Department of Pulmonary and Critical Care Medicine, Asan Medical Center, Seoul, Republic of Korea. Department of Internal Medicine, Seoul National University Boramae Medical Center, Seoul, Republic of Korea. Department of Internal Medicine, Kyung Hee University Hospital at Gangdong, Seoul, Republic of Korea. Department of Internal Medicine, Hanyang University Hospital, Seoul, Republic of Korea.