Legionella test is done to determine the legionella bacteria that may cause pneumonia. Legionnaire’s disease is first discovered in 1976 after a pneumonia outbreak in congress participants , in a legion congress in Philadelphia. Total 182 person were affected from infection and 29 people died. Agent was a new gram negative bacterium type that was never identified before. It is called Legionella pneumophilia according to the outbreak and the disease that it caused. Disease has 2 different forms; Legionella disease ( pneumonia) and Pontiac fever.
Legionella infection chain has 4 rings
1-) Bacteria’s natural environment; rivers, lakes, thermal water, springs
2-) Expansion factor for bacteria growth; air condition systems, cooling towers, hot water tanks, shower heads, hot water taps
3-) Additional mechanisms that help bacteria to reach the sensitive host; legionella bacterium is transported from reservoir by water. Bacterium is transmitted to people in aerosolized water or by directly aspiration, person to person transmission is not determined.
4-) Sensitive host; elder age > 50, gender- men, malignancy, immunosuppressive treatment, diabetes, chronic lung disease, smoking, alcohol usage.
Legionella bacterium is transmitted by respiration of water droplets or vapor and spreads to the lungs. It can be treated by antibiotics but early diagnosis is very important. Legionella infection may be fatal if not treated. Legionella disease may be diagnosed by 3 test types;
Antigen test; determination of a protein that is produced by legionella bacterium
Culture test; identifying the legionella bacteria in sputum, pleural fluid, BAL fluid (bronchoalveolar lavage)
Molecular test; (PCR) determination of bacteria by genetic material
Legionella test samples
Sample type changes according to the test method. Culture and molecular test may be done in sputum and respiratory secretions. Urine sample is needed for antigen test.
Symptoms of legionella disease
- Muscle ache
- Chest pain
- Joint pain
- Shortness of breath
- High fever
- Cough dry or sometimes with blood or mucus
- Loss of appetite
Legionella test types
Polymerase chain reaction may identify bacteria’s genetic material. Respiratory secretions, urine, serum and other body fluids may be used.
Bacteria proteins may be identified by Legionella pneumophilia antigen test. This test is usually done in urine sample.
Legionella culture test is the most reliable test to diagnose the infection of these bacteria type. A special media is used for legionella bacteria growth. It may take 48-72 hours for bacteria growth.
Evaluation of Legionella test results
For the diagnosis of legionella disease; physical examination results, X-ray , and the test result must be be evaluated together. A negative legionella test results doesn’t mean that there is no illness. A different type of legionella bacteria may be the cause of disease, and the tested bacteria type may be different so test result may be found negative. Also so low numbers of bacteria may be found in culture sample and these bacteria may not be enough for bacteria growth. A new sample may be needed for culture test.
If the urine legionella antigen test result is positive this means the cause of pneumonia symptoms is legionella bacterium. Urinary antigen analysis is 90% sensitive and 100% spesific. Antigen can be detected for weeks after acute illness.
Positive culture result and positive PCR test results also mean patient has legionella disease. PCR test is rapid and may detect all species. Negative results does not exclude diagnosis.