Which bodily fluid can be used for a simple, quick, and reliable antigen test to detect Legionella pneumophila serogroup 1?

• A. Blood
• B. Urine
• C. Saliva
• D. Sputum

Answer: (B)

Urine is the best sample for a rapid, simple, reliable antigen test for Legionella pneumophila serogroup 1 because the test detects a soluble bacterial antigen that is shed into the bloodstream and filtered into the urine. This makes collection easy and results fast, which is crucial for guiding early treatment in suspected Legionnaires’ disease. The test is highly specific for serogroup 1, the serogroup most commonly associated with illness. While other specimens like blood or sputum can be used for culture or molecular tests, they are not as convenient or validated for quick antigen detection. Be aware that the test mainly detects serogroup 1 and may miss infections caused by other Legionella serogroups or species, and false negatives can occur early in infection or after antibiotics.