An update on Legionella

Purpose of review: Legionella pneumophila is increasingly recognized as a significant cause of sporadic and epidemic community-acquired and nosocomial-acquired pneumonia. This review focuses on the latest literature concerning the epidemiology, pathogenesis, clinical presentation, diagnosis, and treatment of Legionnaires' disease.

Recent findings: A significant increase in the incidence of Legionnaires' disease in the United States has been documented over the last years. L. pneumophila has recently been found to be a leading cause of community-acquired pneumonia in hospitalized and ambulatory patients in Germany. Recent studies provide insight into the understanding of the pathogenesis of Legionnaires' disease and the relevance of the formation of biofilms. Clinical manifestations of Legionnaires' disease are not specific and current diagnostic scores are of limited use. Several recent studies offer useful information concerning Legionnaires' disease in immunosuppressed patients. A systematic review of English literature performed to assess test characteristics of Legionella urinary antigen has found that the pooled sensitivity of the test was 0.74 and specificity was 0.991. Improved clinical response has been observed for patients with Legionnaires' disease treated with highly active antimicrobial agents against Legionella.

Summary: Legionnaires' disease is a significant health problem in many countries. Clinical manifestations are unreliable in diagnosing Legionnaires' disease. Therefore, diagnostic laboratory tests for Legionella, including the urinary antigen test, should be applied to all patients with pneumonia. Levofloxacin (or other fluoroquinolone) or azithromycin are the current drugs of choice for treatment of Legionnaires' disease. Effective preventive strategies are needed.