Legionella as a cause of severe pneumonia

Legionella pneumophila has been found to be a common cause of community-acquired pneumonia in patients who required intensive care unit (ICU) admission. In many studies, the clinical manifestations for Legionnaires' disease were more severe and the mortality was higher when compared with pneumonias of other etiology. However, this may be due to delay in diagnosis and suboptimal antibiotic therapy, rather than enhanced virulence of L. pneumophila. A syndromic approach using high fever, diarrhea, mental status changes, hyponatremia, etc., may be useful in suggesting the correct diagnosis in patients with severe pneumonia, but this remains to be validated. The availability of Legionella diagnostic microbiology testing in-house (rather than being sent to an outside reference laboratory) maximizes the ability to correctly diagnose Legionnaires' disease. All patients with community-acquired pneumonia admitted to an ICU should undergo Legionella testing using the urinary antigen and culture on selective media. Moreover, we recommend routine cultures of the hospital water supply once a year (regardless of whether a case of nosocomial Legionnaires' disease has ever been diagnosed). If Legionella is found in the water supply, all patients with nosocomial pneumonia should undergo diagnostic tests for Legionella; empiric anti-Legionella antibiotics should be administered pending definitive diagnosis.