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Legionella Testing

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Also known as: Legionella pneumophila; Legionnaires Disease Testing
Formal name: Legionella Antigen, urine; Legionella Culture; Legionella by PCR

The Test Sample

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 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. 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 fountains.

Infections occur when an individual inhales steam, mist, or airborne droplets contaminated with Legionella bacteria. The infection is not spread from one person to another. Pontiac fever typically develops within 24-48 hours while Legionnaires disease develops within a few days to a couple of weeks. According to the Centers for Disease Control and Prevention (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 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 are sporadic, but they may also be seen in outbreaks, and 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.

A few different types of tests are available to help diagnose infections caused by Legionella bacteria:

  • An antigen test that detects a protein made by the bacteria in urine is one of the most common tests.
  • The bacteria may also be detected by culturing sputum, respiratory secretions or other body fluids.
  • A molecular test (polymerase chain reaction, PCR) may be used to identify Legionella in respiratory samples.

How is the sample collected for testing?

The sample collected depends on the test to be performed.

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 doctor'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 doctor.

For antigen testing, a random urine sample is collected in a sterile cup provided by the laboratory or doctor's office.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.