Screening for Legionella antigen in urine is 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 species and 70 serotypes. One species, 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 information on how aerosols and droplets are created, utilizing which microorganisms are dispersed into the atmosphere. Legionnaires' disease can occur after inhaling aerosols containing Legionella microbes or ingesting infected water. Direct transmission of microorganisms (from person to person) does not appear to be a risk.
The likelihood of contracting Legionnaires' disease depends on the degree of water contamination, the sensitivity of the person exposed, and the intensity of exposure. It is characterized as an «opportunistic disease» and usually affects people with 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 severe form with a 10-15% mortality rate. Patients initially develop a cough, fever, and nonspecific symptoms, including discomfort, myalgia, and headache. Some also 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 that of Legionnaires' disease (up to 95% of those exposed).
Various laboratory techniques (culture, direct immunofluorescence, molecular techniques, serological testing, antigen detection) and several biological samples (from the respiratory system, serum, and urine) have been used to diagnose Legionella pneumonia. In general, respiratory specimens are preferred. Unfortunately, one of the symptoms of Legionnaires' disease is the relative lack of productive cough, which often requires invasive procedures to obtain appropriate specimens (e.g., bronchial lavage, aspiration, lung biopsy).
It has been shown that a specific soluble antigen exists in the urine of patients with Legionnaires' disease. The presence of the Legionella antigen in urine (an ideal sample for collection and transport) is significant for detecting the disease in its early and more advanced stages. The antigen can be detected in the urine three days after the onset of symptoms.
Important Note
Laboratory test results are the most critical parameter for diagnosing and monitoring all pathological conditions. Between 70 to 80% of diagnostic decisions are based on laboratory tests. Correctly interpreting 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 analyzed based on each case and family history, clinical findings, and the results of other laboratory tests and information. Your 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 contact your doctor to ensure you receive the best possible medical care.
