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Legionellosis
Last reviewed: 05.07.2025
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Legionellosis (Pittsburgh pneumonia, Pontiac fever, Fort Bragg fever) is a group of diseases caused by bacteria of the genus Legionella, with an aerosol mechanism of transmission of the pathogen, characterized by fever, intoxication, damage to the respiratory tract, kidneys and central nervous system.
Legionella pneumophila most often causes pneumonia with signs of extrapulmonary pathology. Diagnosis requires a special plant medium, serological tests or PCR analysis. Treatment of legionellosis is carried out with doxycycline, macrolides or fluoroquinolones.
ICD-10 codes
- A48.1. Legionnaires' disease.
- A48.2. Legionnaires' disease without pneumonia (Pontiac fever).
What causes legionellosis?
The first appearance of this organism was reported in 1976 at the American Legion convention, hence the name "Legionnaires' disease". Extrapulmonary infection is called Pontiac fever. These bacteria can be found in dirty or raw water. Industrial water storage containers, including air-conditioning units that rely on water cooling, enhance the growth of MO. Spread of infection is most likely through aerosols from drinking water.
Extrapulmonary symptoms of Legionellosis occur most frequently in hospitalized patients and most frequently involve the heart. Other manifestations of infection include the central nervous system, liver, and intestines. Immunocompromised patients, smokers, the elderly, and patients with chronic lung disease are primarily affected.
What are the symptoms of legionellosis?
Legionnaires' disease begins with a flu-like syndrome. Fever, chills, weakness, myalgias, headache, or confusion occur abruptly. Legionellosis symptoms often include nausea, profuse watery diarrhea, abdominal pain, cough, and arthralgias. Pulmonary manifestations may include dyspnea, pleuritic pain, and hemoptysis.
What's bothering you?
How is Legionellosis diagnosed?
Legionellosis is diagnosed by sputum or bronchial washings. Blood culture is unreliable. Slow growth on a nutrient medium may delay identification of the pathogen by 3-5 days. Direct fluorescent staining of sputum or bronchial washings with labeled antibodies is often used. PCR with DNA probing is also available. A urine antigen test has a sensitivity of 70% and a specificity of 100% three days after the onset of symptoms. However, this test only detects Legionella pneumophila (serogroup 1) and is unable to detect non-pneumophilic legionella. A paired antibody test in the acute or convalescent period may provide a delayed diagnosis. A fourfold increase or an antibody titer in the acute period above 1:128 is considered diagnostic. Chest radiograph usually reveals nonspecific changes such as infiltrates and pleural effusion.
How to examine?
What tests are needed?
How is legionellosis treated?
Legionellosis is treated with doxycycline, macrolides, and fluoroquinolones. The recommended treatment is any pulmonary fluoroquinolone (intravenously or orally) for 7-14 days. Rifampin may be added for acute infections. Mortality is low in otherwise healthy individuals, but can reach 50% in hospital-acquired outbreaks.