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Legionellosis or Legionnaires' disease (LD) is a bacterial lung infection characterized by a potentially fatal pneumonia.
ORPHA:549Classification level: Disorder
- Legionnaires disease
- Prevalence: -
- Inheritance: Not applicable
- Age of onset: All ages
- ICD-10: A48.1
- OMIM: -
- UMLS: C0023240 C0023241
- MeSH: D007876 D007877
- GARD: 6876
- MedDRA: 10035718 10061266
The annual notification rate in 2009 from 25 EU Member States amounted to approximately 1/90,000. In France the annual incidence is around 1/50,000.
LD has an incubation period of 2-10 days with fatigue and weakness often being the first signs of the disease. It manifests as pneumonia characterized by fever, cough, sputum production and shortness of breath. Other symptoms can include diarrhea, myalgia, headaches, confusion/delirium and nausea. LD is most severe in elderly and immunocompromised people (due to immunosuppressive therapy, especially with corticosteroids, transplants, hematologic malignancy or cancer), who are an ever-increasing risk group for infection. Other risk factors for LD include cigarette smoking, age over 50, male gender, diabetes, and chronic heart, lung or kidney disease.
LD is caused by Legionella pneumophila (most commonly serogroup 1), a bacteria found in water and wet soil. Humans are infected by inhaling aerosols containing the bacteria, most commonly from showers, hot tubs, saunas or other bathing facilities. The same bacteria are responsible for Pontiac fever (PF; see this term) a mild form of LD. LD occurs sporadically and in outbreaks, with the sporadic form accounting for 65 to 80% of cases. Outbreaks are predominantly linked to contaminated aerosols from wet cooling systems or occur in hospitals, nursing homes or hotels.
EU case definitions have been agreed upon associating clinical and laboratory criteria for case confirmation. Any person with pneumonia and one of the following criteria: isolation of Legionella spp. from respiratory secretions or any normally sterile site, detection of L. pneumophila antigen in urine or L. pneumophila serogroup 1-specific antibody response, are given a diagnosis of LD. Detection of Legionella spp. nucleic acid in a clinical specimen has been added as criteria for probable cases.
The disease has no particular clinical features that clearly distinguish it from other types of pneumonia. Other bacterial (Streptococcus pneumonia, Staphylococcus aureus and Haemophilus influenza) or viral infections that cause pneumonia need to be ruled out.
Management and treatment
Treatment involves antibiotics (usually macrolides and quinolones). Hospitalization is often required. Ventilatory support may be necessary in those with serious breathing difficulties. Legionella surveillance programs are based on notification of cases at a national and European level and on legislation for controlling the development of the bacteria in the aquatic environment.
In most cases, LD is treated and cured with antibiotics but in those with compromised immune systems or underlying health conditions the prognosis can be poor. The overall case fatality rate is around 10-15%.