Nonsevere community-acquired pneumonia - Correlation between cause and severity or comorbidity

Background: Community-acquired pneumonia frequently constitutes a nonsevere infection manageable at home. However, for these low-risk episodes, the ep idemiological features have not been carefully analyzed. Objectives: To determine the cause of nonsevere community-acquired pneumoni a and to investigate if a correlation exists between cause and severity or comorbidity. Methods: During a 3-year period, all patients with nonsevere community-acqu ired pneumonia, according to the Pneumonia Patient Outcome Research Team pr ognostic classification (patients in groups 1-3), were included in the stud y. Causes were investigated through the following procedures: cultures of b lood, sputum, and pleural fluid; serologic tests; and polymerase chain reac tion methods to detect Streptococcus pneumoniae DNA in whole blood or Mycop lasma pneumoniae and Chlamydia pneumoniae DNA in throat swab specimens. Results: Of 317 initially included patients, 247 were eligible for the stud y. A microbial diagnosis was obtained in 162 patients (66%), and the main p athogens detected were S pneumoniae (69 patients [28%]), M pneumoniae (40 p atients [16%]), and C pneumoniae (28 patients [11%]). For the 58 patients i n prognostic group 1, M pneumoniae was the most prevalent cause, and atypic al microorganisms constituted 40 (69%) of the isolated agents. In contrast, for patients in prognostic groups 2 and 3, S pneumoniae was the leading ag ent, and a significant reduction of M pneumoniae cases and a greater presen ce of other more uncommon pathogens were observed. The existence of comorbi d conditions was not a determining factor for particular causes. Conclusions: Among low-risk patients with community acquired pneumonia, the re was a certain correlation between severity and cause. In contrast, the e xistence of a comorbidity did not have a predictive causative value.