Legionella Testing
- Also Known As:
- Legionella pneumophila
- Legionnaires Disease or Legionellosis Testing

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At a Glance
Why Get Tested?
To detect and diagnose Legionella bacteria as the cause of pneumonia or flu-like symptoms; to investigate an outbreak caused by Legionella
When To Get Tested?
When you have a cough, body aches, shortness of breath, headache, and fever with chills, and may have abdominal pain, diarrhea, nausea, and/or mental changes that a healthcare provider suspects may be due to an infection caused by Legionella
Sample Required?
A urine sample, a sputum sample, blood sample, and/or respiratory secretions or other body fluids collected by a healthcare practitioner
Test Preparation Needed?
None
You may be able to find your test results on your laboratory’s website or patient portal. However, you are currently at Testing.com. You may have been directed here by your lab’s website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab’s website or portal, or contact your healthcare practitioner in order to obtain your test results.
Testing.com is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.
The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.
If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.
Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called “normal” values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.
While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are “within normal limits.”
For more information, please read the article Reference Ranges and What They Mean.
What is being tested?
Legionella is a type of bacteria that can cause a serious form of pneumonia called Legionnaires disease. Legionella testing detects the presence of the bacteria or parts of it (antigens) to help diagnose the cause of a person’s pneumonia.
A legionella infection affects the lower respiratory tract, often requires hospitalization, and has a significant mortality rate. In addition to pneumonia, Legionella bacteria can also cause Pontiac fever, a milder and self-limiting illness with flu-like symptoms (without pneumonia). Together, Legionnaires disease and Pontiac fever are referred to as legionellosis.
Legionella bacteria are found naturally throughout the environment. They prefer warm, stagnant water and can grow in the plumbing systems of large buildings such as hotels, hospitals, and cruise ships. The bacteria may contaminate whirlpool spas, drinking and bathing water, hot water tanks, air conditioning cooling towers, ice machines, humidifiers, and public fountains.
Infections occur when an individual inhales airborne water droplets such as steam or mist that are contaminated with Legionella bacteria. The bacteria are not passed from one person to another, but many people can become infected by the same contaminated water source, potentially resulting in a legionellosis outbreak. According to the Centers for Disease Control and Prevention (CDC), legionellosis outbreaks occur any time two or more people become ill in the same place at about the same time.
Legionella infection or Pontiac fever is confirmed when a person showing typical symptoms of the disease has a positive confirmatory laboratory test (usually a positive culture or urine test).
State and local health departments have jurisdiction over legionellosis outbreaks in their state; however, legionellosis is a nationally notifiable disease and state health departments should report all laboratory-confirmed cases to the CDC.
Pontiac fever typically develops within 24-48 hours while Legionnaires disease develops within a few days to a couple of weeks. According to the CDC, about 8,000 to 18,000 people are hospitalized with Legionnaires disease each year. The actual number of people affected by legionellosis is likely much higher as most cases of Pontiac fever and many cases of Legionnaires disease are thought to go undiagnosed.
Although anyone may be affected, adults over 50 are at the highest risk for Legionnaires disease, as are those who smoke, have lung diseases, or have compromised immune systems (such as those with HIV/AIDS, cancer, or who are taking immunosuppressant medications). People with chronic underlying diseases such as diabetes, kidney disease, or liver disease are also more vulnerable, and men are affected more often than women. Most cases of Legionnaires disease are sporadic, but they may also be seen in outbreaks, which typically occur during the summer and early fall. Pontiac fever is frequently linked with outbreaks.
There are many different types of Legionella bacteria, but only a few are common. In the United States, as many as 80% of legionella infections in adults are caused by Legionella pneumophila, serogroup 1 (a subtype of the species). Other serogroups of L. pneumophila, including 4 and 6, cause a number of cases. Other species of Legionella, such as Legionella micdadei, Legionella bozemanii, Legionella dumoffii, and Legionella longbeachae, may cause infections in children and/or are more prevalent in other parts of the world.
How is the sample collected for testing?
The sample collected depends on the test to be performed.
- For antigen testing, a random urine sample is collected in a sterile cup provided by the laboratory or healthcare practitioner’s office.
- For culture or molecular testing, a sputum sample may be expectorated or induced. Expectorated samples are coughed up and expelled into a sterile cup provided by the laboratory or health practitioner’s office. The person’s mouth should be rinsed with water or saline prior to sample collection. Deep coughing is generally required, and the person should be informed that it is phlegm/mucus from the lungs that is necessary, not saliva. If someone cannot produce a sputum sample, then it can often be induced by inhaling a sterile saline or glycerin aerosol for several minutes to loosen phlegm in the lungs. Respiratory secretions, other body fluid samples, and any tissue biopsy samples are collected by a health care practitioner.
Common Questions
View Sources
Sources Used in Current Review
2018 Review completed by Yanal Murad, PhD, D(ABMM).
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Fields B, et al. Legionella and Legionnaires’ Disease: 25 Years of Investigation. Clin Microbiol Rev. 2002 Jul;15(3):506-26. Available online at https://www.ncbi.nlm.nih.gov/pubmed/12097254. Accessed on 11/11/2018.
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Sources Used in Previous Reviews
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Rathore M, Alvarez A. (2015 May 7, Updated). Legionella Infection. Available online at http://emedicine.medscape.com/article/965492-overview. Accessed 8/20/2015.
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