1 Division of Pulmonary, Allergy, Critical Care, and Sleep Medicine, Department of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, USA. Electronic address: yoonjh@upmc.edu.
2 Department of Emergency Medicine, Dong-A University College of Medicine, Busan, South Korea.
3 Department of Social Medicine, Dankook University College of Medicine, Cheon-An, South Korea; The Korean Academy of Medical Sciences, Seoul, South Korea.