Legionella Tests
Reviewed
Also called: Legionnaires' disease testing, Legionellosis testing, Legionella pneumophila
Legionella tests look for these bacteria in urine, sputum, or in some cases in lung tissue.
Specimen: Urine, sputum, or lung tissue (via bronchoscopy/BAL). Blood for exposure assessment only.
Why this test may be ordered
- You have symptoms of Legionnaires' disease (cough, high fever, chills, headache, chest pain, shortness of breath, fatigue, nausea, vomiting, diarrhea, confusion).
- To distinguish Legionnaires' disease from other types of pneumonia, since treatment differs.
- To help confirm the diagnosis in a suspected outbreak or after known exposure to contaminated water.
Preparation and collection
You don't need any special preparations for a Legionella urine test. If you get a BAL and/or bronchoscopy, you may be asked to fast (not eat or drink) for up to twelve hours before the test. You may also need to stop taking certain medicines before a sputum culture and a BAL/bronchoscopy. So, tell your provider about everything you take. Antibiotics may affect bacterial growth and your results, especially those of a sputum culture. But don't stop taking any medicines unless your provider tells you to.
Legionella tests are usually done using urine (pee) and/or sputum. Many providers will test both urine and sputum samples to confirm a diagnosis. A blood test may be done to see if you have been exposed to the bacteria.
There is no risk to providing a urine or sputum sample. There is very little risk to having a blood test. There is very little risk to having a bronchoscopy or a BAL. Serious complications are rare, but they may include bleeding in the airways, infection, or a pneumothorax (collapse of part of your lung).
Understanding results
Your provider may consider your symptoms, medical history, and the results of other tests to understand the results of your Legionella test.
- Positive: If your results were positive, it probably means you have Legionnaires' disease. Limitation: If you have Legionnaires' disease, you may have symptoms such as fatigue and muscle aches for several months after treatment. Next step: Whether your results were positive or negative, your provider may do other tests to confirm or rule out a diagnosis of Legionnaires' disease.
- Negative: If your results were negative, it may mean you have a different type of infection. Limitation: It may also mean not enough Legionella bacteria were found in your sample. Next step: If you have questions about your results, talk to your provider.
- Blood tests only show past exposure, not current infection.
- A negative result does not rule out Legionnaires' disease because the bacteria may not be present in the sample.
- Prior antibiotic use can affect sputum culture results.
- Other tests (e.g., chest X-ray, Gram stain, acid-fast bacillus, sputum culture, respiratory pathogens panel) are often needed to confirm or rule out the diagnosis.
What to do next
Whether your results were positive or negative, your provider may do other tests to confirm or rule out a diagnosis of Legionnaires' disease. If you have questions about your results, talk to your provider.
- What do my symptoms suggest about the likelihood of Legionnaires' disease?
- How do these test results compare with other tests I have had?
- If the test is negative but symptoms continue, what should I do next?
- Are there any follow-up tests I should consider?
Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.