“…Furthermore, Agustí et al reported considerable variation in the risk of COPD exacerbations between patients and described a number of risk factors for exacerbation, including a history of previous exacerbations, age >65 years, COPD severity, high BODE index (body mass index, airflow obstruction, dyspnoea and exercise), poor health status and presence of comorbidities. 37 Although the multiple genetic factors involved in the development of COPD may influence its clinical management, 38 certain environmental characteristics, such as changes in air temperature and increased air pollution, can be associated with acute exacerbations of COPD. 39 It is therefore extremely difficult to compare populations in different studies.…”