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Legionnaires disease was first recognized during a pneumonia outbreak at the Legionnaires convention in Philadelphia in 1976. Investigators with the CDC isolated a novel, gram-negative bacillus, later named Legionella pneumophila. It is now widely recognized that Legionella pneumophila (and other members of the genus Legionella) cause Legionnaires disease.
Sensitive and rapid diagnosis of pneumonia caused by Legionella species
A positive PCR result for the presence of a specific sequence found within the Legionella 5S rRNA gene indicates the presence of a Legionella species DNA, which may be due to Legionella infection or environmental/water Legionella DNA in the specimen.
A negative PCR result indicates the absence of detectable Legionella DNA in the specimen, but does not rule-out legionellosis as false-negative results may occur due to inhibition of PCR, sequence variability underlying the primers and probes, or the presence of Legionella species in quantities less than the limit of detection of the assay.
This assay does not differentiate between the Legionella species. The assay is not recommended as a test of cure because nucleic acid may persist after successful treatment. False-positive results are theoretically possible if patient specimens are contaminated with Legionella DNA, which may occur since Legionella species are environmental organisms present in aquatic environments. The following uncommonly encountered species of Legionella are not detected by this assay: Legionella anisa, Legionella feeleii, Legionella maceachernii, Legionella parisiensis, and Legionella sainthelensi.
1. Hayden RT, Uhl JR, Qian X, et al: Direct detection of Legionella species from bronchoalveolar lavage and open lung biopsy specimens: comparison of LightCycler PCR, in situ hybridization, direct fluorescence antigen detection, and culture. J Clin Microbiol 2001;39(7):2618-2626
2. Diederen BM, Kluytmans JA, Vandenbroucke-Grauls CM, Peeters MF: Utility of real-time PCR for diagnosis of Legionnaires' disease in routine clinical practice. J Clin Microbiol 2008;46(2):671-677
3. MacDonell MT, Colwell RR: The nucleotide sequence of the 5S rRNA from Legionella pneumophila. Nucleic Acids Res 1987;15(3):1335