Seasonality, ambient temperatures and hospitalizations for acute exacerbation of COPD: a population-based study in a metropolitan area

Almagro, Pere; Hernandez, Carme; Martinez-Cambor, Pable; Tresserras, Ricard; Escarrabill, Joan

Most epidemiological studies exploring the influence of temperature on cardiorespiratory diseases have focused mainly on the effect of heat. For example, a recent metaanalysis concerning the relationship between climate and cardiorespiratory morbidity found only three studies that examined the effect of cold in these pathologies. 19 In another study performed in Copenhagen, the authors found a higher prevalence of hospitalizations for respiratory causes in the warmest months. 20 These data are similar to a Canadian study that found an association between colder temperatures and cardiovascular diseases but not with respiratory diseases. 21 In contrast, studies that have specifically analyzed COPD exacerbations show that numbers increase in the winter months, including the number of hospitalizations for exacerbation of COPD. 22 Recently, two publications based on the TORCH and POET trials indicated that the numbers of COPD exacerbations and hospitalizations in winter were almost double those in summer, which is in agreement with our study. Regrettably, both studies were only able to perform the analysis stratified by month and seasonality, and therefore only indirectly considered ambient temperature, due to a lack of climate data analysis. 12, 13 There are very few studies about the role of temperature in the number and severity of COPD exacerbations. A study performed in Bavaria, Germany, showed an increase of 1%