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

Abstract

Background: 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.

Objective: We compared long-term health outcomes of individuals with COPD with and without a history of asthma in a population-based cohort study.

Methods: All individuals with physician-diagnosed COPD between the ages 40 and 55 years 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 2 years 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.

Results: Among 9053 patients with COPD, 2717 (30%) had a history of asthma. Over a median of 2.9 years, 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.

Conclusions: 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.

Keywords: COPD; asthma; hospitalization; mortality.