Atypical pneumonia: recognition and treatment.

While the term "atypical pneumonia" has been in use for many years, it cannot in fact be defined. However, there is a persuasive reason to retain the clinical use of the term, and that is to provide a guide for the clinician in the choice of empirical antibiotic therapy for patients with acute pneumonia. Atypical pneumonia, then, is a descriptive term for a common clinical syndrome. Provided certain clinicoepidemiological groups are excluded, the most common infectious causes of this syndrome are Mycoplasma pneumoniae, Chlamydia psittaci, Coxiella burneti, and Legionella species, but it should be stressed that the syndrome may occasionally be produced by other infectious and non-infectious diseases. Conversely, the atypical pneumonia syndrome occupies only one part of the clinical spectrum of disease that is caused by these organisms. This becomes important when one is selecting antibiotic therapy for patients with other respiratory syndromes, especially those with life-threatening disease. The antimicrobial therapy of the three common causes of atypical pneumonia is discussed in detail.