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. 2015 Dec 16;144(2):507–514. doi: 10.1378/chest.12-2308

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© 2013 The American College of Chest Physicians

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Incidence and prevalence of COPD exacerbations in all study participants by week of the study. The numbers of COPD exacerbations are shown as horizontal bars over the course of the study (December 1, 2001, to April 30, 2009). The length of the bars represents the length of the exacerbation and the colors represent the categories of virus detected in each. Shading signifies the five periods of the study. Numbers in parentheses represent the rate of exacerbations per participant year. The vertical axis shows the number of exacerbations (number/subject) by study period.