Legionella Antigen, Urine

CPT CODE:

USEFUL FOR:

As an adjunct to culture for the presumptive diagnosis of past or current legionnaires' disease (Legionellapneumophila serogroup 1)

SPECIMEN REQUIRED:

0.5 mL from a random urine collection. No preservative. Send specimen refrigerated in a plastic, 13-mL urine tube.

TRANSPORT TEMPERATURE:

Refrig\Frozen OK\Ambient <24 hours OK

CLINICAL INFORMATION:

Legionnaires' disease, named after the outbreak in 1976 at theAmerican Legion convention in Philadelphia, is caused by Legionellapneumophila and is an acute febrile respiratory illness ranging in severity from mild illness to fatal pneumonia. Since that time, it has been recognized that the disease occurs in both epidemic and endemic forms, and that sporadic cases are not readily differentiated from other respiratory infections by clinicalsymptoms. It is estimated that about 25,000 to 100,000 Legionellainfections occur annually. Known risk factors include:immunosuppression, cigarette smoking, alcohol consumption,and concomitant pulmonary disease. The resulting mortality rate,which ranges up to 40% in untreated immunocompetent patients,can be lowered if the disease can be rapidly diagnosed andappropriate antimicrobial therapy instituted early. Legionellapneumophila is estimated to be responsible for 80% to 85% ofreported cases of Legionella infections with the majority of casesbeing caused by Legionella pneumophila serogroup 1 alone.
A variety of laboratory techniques (culture, direct fluorescent antibody, DNA probes, immunoassay, antigen detection), using a variety of specimen types (respiratory specimens, serum, urine), have been used to help diagnose Legionella pneumonia. Respiratory specimens are preferred. Unfortunately, one of the presenting signs of legionnaires' disease is the relative lack of productive sputum. This necessitates the use of invasive procedures to obtain adequate specimens (eg, bronchial washing, transtracheal aspirate, lung biopsy) in many patients. Serology may also be used, but is often retrospective in nature.
It was shown as early as 1979 that a specific soluble antigen waspresent in the urine of patients with legionnaires' disease.(1) Thepresence of  Legionella antigen in urine makes this an idealspecimen for collection, transport, and subsequent detection inearly, as well as later, stages of the disease. The antigen may bedetectable in the urine as early as 3 days after onset of symptoms.

CLINICAL INTERPRETATION:

PositivePresumptive positive for Legionella pneumophila serogroup 1 antigen in urine, suggesting current orpast infection. Culture is recommended to confirm infection.
NegativePresumptive negative for Legionella pneumophilaserogroup 1 antigen in urine, suggesting no recent orcurrent infection. Infection with Legionella cannot beruled out because:-other serogroups (other than serogroup 1, which is  detected by this assay) and other Legionella species  (other than Legionella pneumophila) can cause disease-antigen may not be present in urine in early infection-the level of antigen may be below the detection limit of the testLegionella culture is recommended for cases of suspected Legionella pneumonia due to organisms other than Legionella pneumophila serogroup 1.

REFERENCE VALUES:

Negative (reported as positive or negative)