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We compared risk factors and clinical characteristics, 9-year lung function change and hospitalisation risk across subjects with the asthma-chronic obstructive pulmonary disease (COPD) overlap syndrome (ACOS), asthma or COPD alone, or none of these diseases.
Participants in the European Community Respiratory Health Survey in 1991-1993 (aged 20-44 years) and 1999-2001 were included. Chronic airflow obstruction was defined as pre-bronchodilator forced expiratory volume in 1 s (FEV1)/forced vital capacity<lower limit of normal on both occasions. Based on their history of respiratory symptoms, spirometry and risk factors, subjects were classified as having asthma alone (n=941), COPD alone (n=166), ACOS (n=218) and none of these (n=5659).Subjects with ACOS shared risk factors and clinical characteristics with subjects with asthma alone, but they had an earlier age of asthma onset. FEV1 change in the ACOS group (-25.9 mL·year(-1)) was similar to that in the asthma group (-25.3 mL·year(-1)), and lower (p<0.001) than in the COPD group (-37.3 mL·year(-1)). ACOS was associated with the highest hospitalisation rate.Among young adults aged 20-44 years,
ACOS seems to represent a form of severe asthma, characterised by more frequent hospitalisations, and to be the result of early-onset asthma that has progressed to fixed airflow obstruction.
