What is the recommended procedure for collecting a Legionnaires' (Legionella) test?

Legionella Testing Collection Procedures

For diagnosing Legionnaires' disease, urine should be collected for antigen testing as the primary specimen, along with respiratory specimens (sputum or bronchoalveolar lavage) for culture on selective media before antibiotic administration. 1

Specimen Collection Protocol

Urine Collection

• Collect a clean-catch midstream urine sample in a sterile container
• Volume needed: 3-10 mL of urine
• Consider urine concentration to improve sensitivity (86.6-88.8% in concentrated vs. 63.7-66.6% in unconcentrated samples) 2
• Urine specimens can detect L. pneumophila serogroup 1 antigen 6-14 days after infection onset 2, 1
• Results are available within hours using immunochromatographic or EIA formats 2

Respiratory Specimen Collection

• Collect before initiating antibiotic therapy whenever possible 1
• Options include:
  • Expectorated sputum: Instruct patient to take deep breaths and cough deeply to produce lower respiratory secretions (not saliva)
  • Induced sputum: If patient cannot produce sputum naturally
  • Bronchoalveolar lavage (BAL): For patients who cannot produce adequate sputum samples
• Specimens should be promptly transported to the laboratory for culture on selective media (BCYE with antibiotics) 3
• Culture remains the gold standard with highest specificity, though results take 3-7 days 1

Testing Approach

Primary Tests

1. Urinary antigen testing: Most helpful rapid diagnostic test, particularly sensitive for L. pneumophila serogroup 1 2, 1
2. Culture of respiratory specimens: Should be performed even if urinary antigen is positive to identify specific strains and detect non-serogroup 1 infections 1

Supplementary Tests

• PCR testing: Higher sensitivity for non-serogroup 1 infections, though not FDA-cleared 1
• Serologic testing: Not useful for initial management due to delayed results (requires paired samples 2-4 weeks apart) 1
• Direct fluorescent antibody (DFA): Can be performed on respiratory specimens but has variable sensitivity 3

Important Considerations

• No single test detects all cases of Legionnaires' disease; a combination of tests increases diagnostic yield 1
• Urinary antigen testing is highly sensitive for severe Legionnaires' disease (88-100%) but less sensitive for mild disease (40-53%) 2
• Current urinary antigen tests primarily detect L. pneumophila serogroup 1, which causes most infections, but may miss other serogroups and species 2, 4
• Culture is essential for epidemiological investigations to match patient isolates with environmental sources 3
• Treatment should not be delayed while awaiting test results if Legionnaires' disease is clinically suspected 1

Common Pitfalls to Avoid

• Relying solely on urinary antigen testing, which may miss non-serogroup 1 L. pneumophila and other Legionella species 4
• Delaying specimen collection until after antibiotic administration, which reduces culture sensitivity
• Collecting only upper respiratory specimens (like throat swabs), which have poor yield
• Failing to request Legionella-specific culture media (BCYE), as Legionella won't grow on standard media
• Interpreting a single elevated antibody titer as diagnostic of infection 2

Following this comprehensive testing approach ensures the highest diagnostic yield for Legionnaires' disease, enabling prompt treatment and improved patient outcomes.