Blood eosinophil count and risk of pneumonia hospitalisations in individuals with COPD

Abstract

Blood eosinophil count in chronic obstructive pulmonary disease (COPD) is associated with higher exacerbation rate and favourable response to corticosteroids; however, frequent exacerbations and use of inhaled corticosteroids could elevate pneumonia risk. We tested the hypothesis that high blood eosinophil counts are associated with high risk of pneumonia in individuals with severe COPD from the general population.We included 7180 individuals with COPD from the Copenhagen General Population Study, including 643 with forced expiratory volume in 1 s (FEV₁) <50% predicted between 2003 and 2011. All primary discharge diagnoses of pneumonia during follow-up were recorded.Among individuals with COPD and FEV₁ <50% pred, the multivariable adjusted incidence rate ratio was 2.17 (95% CI 1.31-3.58) for pneumonia comparing individuals with blood eosinophil counts ≥0.34×10⁹ cells·L^-1versus <0.34×10⁹ cells·L^-1 In individuals with clinical COPD, defined by recent exacerbation, ≥10 pack-years of smoking and FEV₁ <70% pred, the corresponding risk was 4.52 (2.11-9.72). Risk of pneumonia did not differ by blood eosinophil count in individuals with COPD and FEV₁ ≥50% pred.In individuals with COPD and FEV₁ <50% pred, blood eosinophil count ≥0.34×10⁹ cells·L^-1 was associated with high risk of hospitalisation due to pneumonia.