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

The presence of comorbidities was collected using secondary diagnoses with ICD9-CM grouped up to a total of 22 diseases. We also calculated the Deyo-Charlson Index, an adaptation of the Charlson Comorbidity Index for use in administrative databases. 14 Temperature data were obtained from a meteorological station located in the Barcelona metropolitan area (Valles Occidental) via the Meteorological Service of Catalonia (www.meteo.cat). The data collected included mean, minimum, and maximum temperatures, along with humidity and precipitation. In order to decrease the noise, these values were considered by weekly means. In addition, to compare our results with those published in the TORCH and POET trials, the numbers of hospitalizations for COPD were also stratified by month and seasonality. Seasons were defined as follows: winter (December to February), spring (March to May), summer (June to August), and autumn (September to November). 12, 13 The rate of respiratory infections was obtained using data collected in the information plan for acute respiratory infections in Catalonia (PIDIRAC). 15 The PIDIRAC data are part of the European Influenza Surveillance Scheme, pertaining to the European Centre for Disease and Control, and its methodology is similar throughout Europe. 16 Briefly, the PIDIRAC receives information from a sentinel network of primary care and pediatric physicians who collect the number of ambulatory consultations and home visits for influenza-like illness, with a collection of the first two weekly respiratory samples by nasal and pharyngeal swabs for viral detection by immunofluorescence or viral polymerase chain reaction. All hospitalizations for influenzalike illness were also studied for respiratory samples, and all positive cases for influenza virus were notified.