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Legionella pneumophila, Antigen

Screening for Legionella antigen in urine is used as an adjunct test to diagnose and evaluate patients with possible legionellosis.

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Legionella pneumophila is an aerobic, Gram-negative, optionally intracellular microbe. Microorganisms are found in freshwater environments worldwide and can cause respiratory disease (Legionnaires' disease). Legionella was first identified after pneumonia broke out in the American Legion in 1976 at a Philadelphia hotel.

The genus Legionella currently includes at least 50 different species consisting of 70 different serotypes. One species of the genus Legionella, L. pneumophila, is the causative agent for approximately 90% of cases of Legionnaires' disease, and serotype 1 (SG1) represents approximately 84% of these cases.

Legionella pneumonia multiplies at temperatures between 25 and 42°C, with an optimum growth temperature of 35°C. Legionella grows in stagnant waters in the environment and in artificial systems, such as cooling towers, condensers, hot and cold water systems, and swimming pools and spas that mimic the natural environment in which the organism thrives. These systems also provide the means by which aerosols and droplets are created by means of which the microorganism is dispersed into the atmosphere. Legionnaires' disease can occur after inhalation of aerosols containing Legionella microbes or after ingestion of infected water. Direct transmission of microorganisms (from person to person) does not appear to be a risk.

The likelihood of being infected by Legionnaires' disease depends on the degree of water contamination, the sensitivity of the exposed person, and the intensity of exposure. Legionnaires' disease is characterized as an «opportunistic disease» and usually affects people who have an underlying disease or a weakened immune system. Predisposing risk factors include advanced age, male gender, smoking, alcohol abuse, chronic lung disease, immunosuppressive therapy, chemotherapy, organ or bone marrow transplantation, and corticosteroid therapy.

Legionellosis can occur as two separate clinical entities: Legionella pneumonia (Legionnaires' disease) with an incubation period of approximately 2-10 days (up to 16-20 days) and Pontiac fever (with an incubation period usually 12-48 hours).

Legionella pneumonia is a serious form of pneumonia with mortality rates of 10-15%. Patients with pneumonia initially develop a cough, fever, and nonspecific symptoms that include discomfort, myalgia, and headache. Some patients have chills, chest pain, diarrhea, delirium, or other neurological symptoms.

Pontiac fever is a milder form of the disease, with no manifestations of pneumonia and usually appears as influenza. It is usually a self-limiting disease and most times no treatment is required. The infestation rate is much higher than Legionnaires' disease (up to 95% of those exposed).

A variety of laboratory techniques (culture, direct immunofluorescence, molecular techniques, serological testing, antigen detection) and a variety of different biological samples (from the respiratory system, serum, urine) have been used for the diagnosis of Legionella pneumonia. In general, respiratory specimens are preferred. Unfortunately, however, one of the symptoms of Legionnaires' disease is the relative lack of productive cough, which often requires the use of invasive procedures to obtain appropriate specimens (eg bronchial lavage, aspiration, lung biopsy).

It has been shown that there is a specific soluble antigen in the urine of patients with Legionnaires' disease. The presence of the Legionella antigen in the urine (an ideal sample for collection and transport) is very important for the detection of the disease in the early stages as well as in the more advanced stages of the disease. The antigen can be detected in the urine 3 days after the onset of symptoms.



Important Note

Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. The correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".

Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings, and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.

At Diagnostiki Athinon we answer any questions you may have about the test you perform in our laboratory and we contact your doctor to get the best possible medical care.

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