LEGIONELLA LABORATORY TESTING
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Indications for Legionnaires’ Disease Testing Listed below are indications that warrant testing patients with pneumonia for Legionnaires’ disease: •
Patients who have failed outpatient antibiotic treatment for community-acquired pneumonia.
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Patients with severe pneumonia, in particular those requiring intensive care.
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Immunocompromised patients with pneumonia.
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Patients with a travel history (patients who have traveled away from their home overnight within 14 days before symptom onset).
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Hospitalized patients with healthcare-associated pneumonia (pneumonia with onset ≥48 hours after admission) at risk for Legionnaires’ disease.
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Patients with an overnight stay in a healthcare facility within 14 days before symptom onset.
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Patients with an epidemiologic link to a setting with a confirmed source of Legionella or that has been associated with at least one laboratory-confirmed case of Legionnaires’ disease
Preferred Diagnostic Tests Culture Isolation of Legionella on media that supports growth of Legionella (i.e., Buffered Charcoal Yeast Extract [BCYE] agar) is confirmatory and an important method for diagnosis. Isolation of Legionella can come from lower respiratory secretions, lung tissue, pleural fluid, or a normally sterile site. Culturing specimens can detect Legionella species and serogroups that the urinary antigen test does not.
Urinary Antigen Test The most commonly used laboratory test for diagnosis of Legionnaires’ disease is the urinary antigen test (UAT), which detects a molecule of the Legionella bacterium in urine. If the patient has pneumonia and the test is positive, then you should consider the patient to have Legionnaires’ disease. The test can remain positive for a few weeks after infection, even with antibiotic treatment. The UAT detects the most common cause of Legionnaires’ disease, L. pneumophila serogroup 1. However, all species and serogroups of Legionella are potentially pathogenic, so a patient with a negative urinary antigen result could have Legionnaires’ disease caused by other Legionella species or serogroups, which is why using culture and UAT in combination is recommended.
Sensitivity and Specificity of Diagnostic Tests Sensitivity varies depending on the quality and timing of clinical specimen collection, as well as technical skill of the laboratory worker performing the test. The table below provides general ranges for the sensitivity and specificity of each diagnostic test.
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Culture Urinary antigen for L. pneumophila serogroup1 (Lp1) Polymerase Chain Reaction (PCR)2 Direct Fluorescent Antibody (DFA) Stain Paired serology
Treatment If your patient has Legionnaires’ disease, please see the most recent IDSA-ATS guidelines for treatment of community-acquired pneumoniaexternal icon and the most recent IDSA-ATS guidelines for treatment of hospital-acquired pneumoniaexternal icon. Note that first line treatment, however, does not always include Legionella-directed antibiotics (e.g., macrolides and respiratory fluoroquinolones). While it is preferred that you obtain diagnostic testing before antibiotic administration, antibiotic treatment should not be delayed to facilitate this process. If your patient has Pontiac fever, antibiotic treatment should not be prescribed. It is a self-limited illness that does not benefit from antibiotic treatment. Patients usually recover within 1 week.
Prevention
Minimizing Legionella growth in complex building water systems and devices is key to preventing infection. Timely identification and reporting of legionellosis cases are also important because this allows public health officials to act quickly. This way they can identify and stop potential clusters and outbreaks by linking new cases to previously reported ones.
About biosan
Biosan Laboratories is an environmental microbiology laboratory that was founded by Dr. Harold Rossmoore in 1973. Our initial microbiology lab was in Ferndale, Michigan where we remained until 1994. Since we knew many of our lab customers would benefit from the ability to perform microbiology testing on-site, Biosan developed several bacteria and fungi test kits for industrial fluids.
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Location Biosan Laboratories, Inc. 1950 Tobsal Court, Warren, MI 48091-1351 USA
Call Us 800-253-6800, 586-755-8970
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