Legionella Tests
Legionella tests are used to diagnose Legionnaires' disease, a severe form of pneumonia caused by bacteria found in contaminated water systems.
What are Legionella tests?
Legionella is a type of bacteria that can cause Legionnaires' disease, a severe pneumonia, or Pontiac fever, a milder flu-like illness. Together, these are known as legionellosis. The bacteria are found in freshwater and can spread through man-made water systems like plumbing, hot tubs, and air-conditioning systems. Infection occurs when people breathe in mist or water droplets containing the bacteria; it does not spread from person to person.
Other names: Legionnaires' disease testing, Legionellosis testing, Legionella pneumophila
Why do I need a test?
You may need testing if you have symptoms of Legionnaires' disease, which typically appear 2–14 days after exposure:
- Cough and chest pain
- High fever and chills
- Headache and fatigue
- Shortness of breath
- Nausea, vomiting, and diarrhea
- Confusion
Testing is critical because Legionnaires' disease can be fatal if not treated promptly with antibiotics.
What happens during the test?
Tests are usually performed on urine or sputum (mucus from the lungs). A blood test may also be used to check for prior exposure, though it cannot diagnose an active infection.
- Urine test: A "clean catch" method is used to ensure the sample is not contaminated by skin germs.
- Sputum test: You may be asked to cough deeply into a cup. If you cannot produce enough sputum, a salty mist may be used to help.
- Bronchoscopy/BAL: If other methods fail, a provider may perform a bronchoscopy, where a thin, lighted tube is inserted into the airways. A bronchoalveolar lavage (BAL) may be performed during this procedure to wash the airways with saline and collect a sample directly from the lungs.
Preparation and Risks
No special preparation is needed for a urine test. For sputum or bronchoscopy, you may need to fast or increase water intake. Inform your provider of all medications, as antibiotics can affect results.
Urine and sputum collection carry no risk. Blood tests carry minimal risk of bruising. Bronchoscopy and BAL carry rare risks, including airway bleeding, infection, or a collapsed lung (pneumothorax).
What do the results mean?
A positive result likely indicates Legionnaires' disease. A negative result may suggest a different type of infection or that insufficient bacteria were present in the sample. Your provider will interpret these results alongside your medical history and other diagnostic tools, such as chest X-rays or bacterial cultures.