[Comparative study of clinical features of typical and atypical pneumonias]

We prospectively analyzed the clinical and laboratory features of 74 patients with community-acquired pneumonia who required hospitalization between May 1996 and October 1997. Typical pathogens were identified in 47, and atypical pathogens in 27. The average age was higher in patients affected by typical pathogens (73.9 years), than in patients affected by atypical pathogens (50.9 years). Univariable analysis found that atypical pneumonias were more frequent in healthy patients than typical pneumonias. Moreover, the presence of relatives with symptoms of airway infection, headache, and earache was more common among the patients with atypical pneumonias, while leukocytosis and elevated C-reactive protein levels were more frequent among patients with typical pneumonias. Typical pathogens accounted for up to 79.6% of the cases of pneumonia with in older patients (aged 60 years or more), whereas atypical pathogens accounted for up to 80% of the cases of pneumonia in younger patients (aged under 60 years). This difference was statistically significant. Of all 74 patients, 39 (52.7%) were afflicted by severe community-acquired pneumonia, as categorized by American Thoracic Society guidelines. The most common pathogen among these patients was Streptococcus pneumoniae. Legionella was one of the top four. Selection of the initial antimicrobial treatment is an important clinical decision that should be made on the basis of clinical features at admission, age, and severity of the patient's illness.