Exacerbations were defined as an increase in severity or new onset of two or more respiratory symptoms (cough, sputum, wheezing, dyspnea, or chest tightness) lasting for at least 3 days and requiring treatment with antibiotics or systemic glucocorticoids.26 Exacerbation severity was graded according to the following scale: mild (required only home management, with or without contact with a health care provider), moderate (required a visit to an emergency department), severe (required hospitalization), and very severe (required intubation and mechanical ventilation).