Legionellosis other diagnostic studies
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Sputum culture and urine antigen testing are the two preferred diagnostic studies. Serologic assays should be used if both culture and urine antigen test are negative in the presence of clinical or epidemiologic clues. For patients who are more likely to have infection not caused by Lp serogroup 1, the best laboratory tests may be sputum culture and PCR.
Other Diagnostic Studies
Sampling
Bronchoalveolar Lavage
Bronchoalveolar lavage (BAL) fluids can be submitted for cultures and PCR in pediatric patients.
Thoracocentesis
Thoracocentesis may be performed to obtain pleural fluid samples in the presence of significant effusion.
Assay
Polymerase Chain Reaction
Polymerase chain reaction (PCR) is used to detect DNA of Legionella in urine, blood, pleural fluid, or bronchoalveolar lavage samples. PCR is an alternative tool for rapid Legionella detection in environmental water. The detection rate of Legionella DNA by qualitative PCR is usually high, at > 90% of positive samples.
Culture
Expectorated sputum, endotracheal aspirates, pleural fluid, blood, or tissue samples may be sent for culture. Unlike serology and urine antigen testing, the yield of cultures is independent of serotype and may be positive in cases of non-Legionella pneumophila species.
Urinary antigen testing
Urine antigen testing is most sensitive for the detection of the Pontiac subtype of Legionella pneumophila serogroup 1. Tests to detect L. pneumophila SG 1 antigen in urine allows for early diagnosis.
Immunofluorescent microscopy
Detection of Lp in respiratory tract tissues and fluids using immunofluorescent microscopy (DFA) may be useful in fixed lung specimens.
Serology
Measurement of antibodies to serogroup 1 often has a low sensitivity and specificity unless paired acute and convalescent sera are tested.