The role of atypical pathogens in community-acquired pneumonia.

The atypical pathogens in community-acquired pneumonia traditionally have included Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella spp. Recent studies documenting their epidemiology and clinical characteristics have shown that these organisms are indistinguishable from the pneumococcus. Furthermore, therapy no longer depends on the specific bacterial cause of community-acquired pneumonia. Etiologic diagnosis is still difficult, although new methods are becoming available. This article focuses on these issues and on why the term atypical is no longer meaningful.