Disease burden of eosinophilic airway disease: Comparing severe asthma, COPD and asthma-COPD overlap

Background and objective There is less understanding of phenotypes and disease burden in asthma-COPD overlap (ACO) than either disease alone. Blood eosinophils may help identify the patients in the clinic with eosinophilic airway inflammation. The potential value of this approach requires an understanding of the illness burden associated with eosinophilic ACO, eosinophilic severe asthma and eosinophilic COPD, defined by blood eosinophils. Methods Participants from studies of multidimensional assessment in airway disease were pooled to identify patients with ACO (n = 106), severe asthma (n = 64) and COPD alone (n = 153). Patients were assessed cross-sectionally for demographic and clinical characteristics, including disease burden indicators such as health-related quality of life (HRQoL) and past-year exacerbation. Eosinophilic patients were identified using different thresholds of blood eosinophil count. Results Using a blood eosinophil count >= 0.3 x 10(9)/L, 41% had eosinophilic airway disease: 55% in ACO, 44% in severe asthma and 29% in COPD. Blood and sputum eosinophils were moderately correlated (r(s) = 0.51, n = 257, P < 0.001). Burden of disease was similar between eosinophilic and non-eosinophilic airway diseases, with poor HRQoL and high number of past-year exacerbations. Burden of disease was similar across eosinophilic severe asthma, COPD and ACO. Eosinophilic COPD tended to have poorer health status than eosinophilic ACO and severe asthma; however, in context of a high prevalence of eosinophilic ACO, cumulative population-level burden of eosinophilic disease was greater in ACO. Conclusion Disease burden across eosinophilic ACO, eosinophilic severe asthma and eosinophilic COPD was high, particularly cumulative population-level burden in ACO. Factors beyond airway inflammation may drive disease burden in severe patients.