Severe COPD cases from Korea, Poland, and USA have substantial differences in respiratory symptoms and other respiratory illnesses.
Kim WJ, Yim JJ, Kim DK, Lee MG, Fuhlbrigge AL, Sliwinski P, Hawrylkiewicz I, Wan ES, Cho MH, Silverman EK. Severe COPD cases from Korea, Poland, and USA have substantial differences in respiratory symptoms and other respiratory illnesses. Int J Chron Obstruct Pulmon Dis. 2017; 12:3415-3423.