Rapid tests for the diagnosis of Legionella infections

Three rapid tests are now available for the diagnosis of Legionella infections: direct fluorescent antibody (DFA) assay, culture on selective media, and urinary antigen detection. A combination of the three tests constitutes a "Legionella Panel." The objective of this article is to present our experience with these assays and to discuss experimental tests that may further improve our capability to diagnose Legionnaires' disease. Diagnoses of Legionella infections were done in 11 of 549 Legionella panels submitted to our reference laboratory. Six were positive for urinary antigen with corresponding negative DFA and culture; three had a positive DFA with negative culture and urinary antigen; and two had positive reactions for all three tests. The use of the Legionella panel offers a rapid, sensitive, and specific diagnosis of infection. The amplification of Legionella DNA in respiratory samples by the polymerase chain reaction method is a new diagnostic test that will further improve our ability to recognize and treat patients with Legionella infections.