The impact of a history of asthma on long-term outcomes of people with newly diagnosed chronic obstructive pulmonary disease: A population study

Abstract

Little is known about the natural history of chronic obstructive pulmonary disease (COPD) that has developed from airway remodeling due to asthma, as compared with other COPD phenotypes. We compared long-term health outcomes of individuals with COPD with and without a history of asthma in a population-based cohort study. All individuals with physician-diagnosed COPD between the ages 40 and 55years from 2009 and 2011 were identified and followed until March 2013 through provincial health administrative data (Ontario, Canada). The exposure was a history of asthma at least 2years before the diagnosis of COPD to ensure it preceded COPD. The hazards of COPD-, respiratory-, and cardiovascular (CV)-related hospitalizations and all-cause mortality were compared between groups using a Cox regression model controlling for demographic characteristics, comorbidities, and level of health care. Among 9053 patients with COPD, 2717 (30%) had a history of asthma. Over a median of 2.9years, 712 (8%) individuals had a first COPD hospitalization, 964 (11%) a first respiratory-related and 342 (4%) a first CV-related hospitalization, and 556 (6%) died. Controlling for confounding, a history of asthma was significantly associated with COPD and respiratory-related hospitalizations (hazard ratio, 1.53 [95% CI, 1.29-1.82] and hazard ratio, 1.63 [95% CI, 1.14-1.88], respectively), but not with CV-related hospitalizations or all-cause mortality. Additional analyses confirmed that these findings were not likely a result of unmeasured confounding or misclassification. Middle-aged individuals with physician-diagnosed COPD and a history of asthma had a higher hazard of hospitalizations due to COPD and other respiratory diseases than did those without.