Acute Pneumonia and Importance of Atypical Bacteria

The term and concept of atypical pneumonia appeared in the 1940s following observations of penicillin-resistant pneumonia [1]. Despite the identification of a large number of microorganisms, the challenge of isolating so-called ‘atypical’ bacteria is the principal cause of failure of the etiologic diagnosis of pneumonia. These pathogenic agents in the tracheobronchial tree include a large variety of bacteria, viruses and even protozoa. Among atypical bacteria, Chlamydia pneumoniae, Mycoplasma pneumoniae, Legionella pneumoniae, Bordetella pertussis, and Coxiella burnetii are the most widespread. Numerous other bacteria are emerging pathogenic species whose virulence is currently being evaluated. Clinical examination only provides a diagnostic orientation in a restricted number of cases. The availability of rapid and specific microbiologic examination improves the diagnostic performance for this type of pneumonia (Table 1) [2]. Since most of these bacteria are intracellular, diagnosis is based principally on serology.