Epidemiology of ACO from Global Data: Does the Prevalence of ACO Vary Among Global Analyses?

Both asthma and chronic obstructive pulmonary disease (COPD) are well-recognized common pulmonary diseases with different pathophysiologies. Some patients have persistent airflow limitation with coexisting asthma and COPD characteristics, and this condition is called asthma and COPD overlap (ACO). Like asthma and COPD, ACO is considered a heterogenous disease, which makes it difficult to understand the underlying disease mechanism. The prevalence of ACO has varied widely in studies, since there is no universal consensus on definition of and diagnostic criteria for ACO, and its prevalence has been roughly estimated at around 2% in the general population, around 25% in asthma patients, and 30% in COPD patients. The frequency and prognosis of ACO patients were reported to have conflicting results. In general, patients with ACO have more severe symptoms, poor quality of life, rapid lung function decline, lower respiratory function, frequent exacerbations, and hospitalizations compared to patients with asthma or COPD alone; however, the exact disease burden for ACO has not been clarified. It is important to clarify the pathophysiology of ACO and conduct a cohort study and clinical trials using established definitions and diagnostic criteria for pathophysiology, biomarkers and objective measures. This would lead to good clinical practice for ACO patients.