Legionnaires' disease | |
---|---|
Other names | Legionellosis,[1] legion fever |
![]() | |
Chest X-ray of a severe case of legionellosis upon admission to the emergency department | |
Specialty | Infectious disease, pulmonology |
Symptoms | Cough, shortness of breath, fever, muscle pains, headaches[2] |
Usual onset | 2–10 days after exposure[2] |
Causes | Bacteria of the Legionella type (spread by contaminated mist)[3][4] |
Risk factors | Older age, history of smoking, chronic lung disease, poor immune function[5] |
Diagnostic method | Urinary antigen test, sputum culture[6] |
Prevention | Good maintenance of water systems[7] |
Treatment | Antibiotics[8] |
Prognosis | 10% risk of death[8] |
Frequency | ~13,000 severe cases a year (US)[9] |
Legionnaires' disease is a form of atypical pneumonia caused by any species of Legionella bacteria,[3] quite often Legionella pneumophila. Signs and symptoms include cough, shortness of breath, high fever, muscle pains, and headaches.[2] Nausea, vomiting, and diarrhea may also occur.[1] This often begins 2–10 days after exposure.[2]
A legionellosis is any disease caused by Legionella, including Legionnaires' disease (a pneumonia) and Pontiac fever (a related upper respiratory tract infection),[10] but Legionnaires' disease is the most common, so mentions of legionellosis often refer to Legionnaires' disease.
The bacterium is found naturally in fresh water.[4] It can contaminate hot water tanks, hot tubs, and cooling towers of large air conditioners.[4] It is usually spread by breathing in mist that contains the bacteria.[4] It can also occur when contaminated water is aspirated.[4] It typically does not spread directly between people, and most people who are exposed do not become infected.[4] Risk factors for infection include older age, a history of smoking, chronic lung disease, and poor immune function.[5][11] Those with severe pneumonia and those with pneumonia and a recent travel history should be tested for the disease.[12] Diagnosis is by a urinary antigen test and sputum culture.[6]
No vaccine is available.[7] Prevention depends on good maintenance of water systems.[7] Treatment of Legionnaires' disease is with antibiotics.[8] Recommended agents include fluoroquinolones, azithromycin, or doxycycline.[13] Hospitalization is often required.[12] The fatality rate is around 10% for healthy persons and 25% for those with underlying conditions.[8]
The number of cases that occur globally is not known.[1] Legionnaires' disease is the cause of an estimated 2–9% of pneumonia cases that are acquired outside of a hospital.[1] An estimated 8,000 to 18,000 cases a year in the United States require hospitalization.[9] Outbreaks of disease account for a minority of cases.[1][14] While it can occur any time of the year, it is more common in the summer and autumn.[9] The disease is named after the outbreak where it was first identified, at a 1976 American Legion convention in Philadelphia.[15]