Do seasonal changes and climate influence the etiology of community acquired pneumonia?

Community acquired pneumonia (CAP) is a highly prevalent pathology whose etiology is determined by the characteristics of the geographic region, and the patient. The study of these features is essential for a proper therapeutic approach. Our aim was to study the changes of the causative agent of CAP brought about by the influence of seasonal and climatic changes in our geographic area.

A prospective and longitudinal study of patients admitted with CAP was done from January 2006 to December 2009. We analyzed demographic data, comorbidities, severity, etiologic agent, complications and mortality. We correlated mean temperature and mean cumulative rainfall for each season with Streptococcus pneumoniae and Legionella pneumophila. Statistical analyses included: Chi squared test, Student's t test for independent samples, variance analysis and Spearman's correlation.

We included 243 patients, 64.6% men and 54.7% over the age of 65. The highest incidence of CAP was in the winter. Streptococcus pneumoniae was the most common causative agent for all seasons except in summer when the main agent was Legionella pneumophila. We observed a significant correlation between the lowest seasonal average temperature and pneumococcal etiology of CAP; inversely, with higher temperatures, Legionella pneumophila was more common. No etiological differences were found by season when related with environmental humidity.

In our area, Streptococcus pneumoniae was the most common etiological agent in winter with low temperatures; in summer, with high temperatures, the most frequent was Legionella pneumophila.