Legionella is a bacterium that causes, among other, a very dangerous form of pneumonia. Legionella is in some aspects similar to chlamydia – it is also an intracellular parasite, i.e. the microorganisms live and multiply within the cells. Legionella species was discovered in 70s of the 20th century in U.S. in Philadelphia in a hotel where a reunion of old legionnaires took place. Many seniors fell ill with pneumonia with a very severe course causing dozens of deaths. The originator of this newly named “Legionnaires' disease” was previously unknown bacterium named Legionella pneumophila.
Legionella likes moist environment, especially slightly heated water (approximately 40-45°C). In places of accommodation (hotels, hospitals, etc) the bacterium survives in water pumps, in air-conditioning, in showers, etc. A person gets infected by inhaling the bacteria (when showering) or drinking the contaminated water. Legionella gets to the nasopharynx, larynx and further into the lower respiratory tract. The lung form of Legionella infection occurs more frequently in the elderly and patients with weakened immunity.
Legionnaires' disease manifests with symptoms of atypical pneumonia (common in viral infections). The symptoms include dry and irritating cough, chest pain, headache, fever, joint and muscle pain, etc. More severe course of the disease may include confusion, vomiting, acute kidney and liver failure. In young and healthy people, Legionella causes a disease known as Pontiac fever. It is not dangerous and it usually manifests only with fever, headache, joint pain and muscle pain. This form of the disease withdraws within days from the onset of symptoms and it shows no signs of lung affection.
In addition to the symptoms of pneumonia, there is elevated CRP and chest X-ray (or other imaging methods) confirms the presence of lung infection. However, it is practically impossible to distinguish Legionella pneumonia from the others by such basic examination methods. Legionella presence may be confirmed serologically from a blood test (finding antibodies against Legionella) and Legionella antigen may be found in urine.
The only way is to keep adequate hygienic standards when managing water sources and cooling systems in hospitals and places of accommodation and regularly take samples from local water sources and cooling systems and check for the presence of Legionella.
The treatment is primarily antibiotic (macrolide and tetracycline antibiotics are especially effective) with symptomatic therapy of symptoms of pneumonia and respiratory insufficiency. In severe case, it is sometimes necessary to ensure proper oxygenation by artificial lung ventilation.