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Legionnaires' disease, also known as legionellosis or Legion fever, is a form of atypical pneumonia caused by any type of ''Legionella'' bacteria. Over 90% of cases of Legionnaires' disease are caused by ''Legionella pneumophila.'' Other causative species include ''L. longbeachae'', ''L. feeleii'', ''L. micdadei'', and ''L. anisa''. These species cause a less severe infection known as Pontiac fever, which resembles acute influenza. These bacterial species can be water-borne or present in soil, whereas ''L. pneumophila'' has only been found in aquatic systems, where it is symbiotically present in aquatic-borne amoebae. It thrives in temperatures between 25 and 45 °C (77 and 113 °F), with an optimum temperature of 35 °C (95 °F). During infection, the bacterium invades macrophages and lung epithelial cells and reproduces within the infected cells. ==Signs and symptoms== The length of time between exposure to the bacteria and the appearance of symptoms is generally two to 10 days, but can rarely extend to as much as 20 days. For the general population, among those exposed between 0.1 to 5% develop disease, while among those in hospital between 0.4 to 14% develop disease.〔 Those with Legionnaires' disease usually have fever, chills, and a cough, which may be dry or may produce sputum. Almost all with Legionnaires' experience fever, while approximately half have cough with sputum, and one third cough up blood or bloody sputum. Some also have muscle aches, headache, tiredness, loss of appetite, loss of coordination (ataxia), chest pain, or diarrhea and vomiting. Up to half of those with Legionnaires' have gastrointestinal symptoms, and almost half have neurological symptoms,〔 including confusion and impaired cognition.〔Edelstein PH. Legionnaires Disease: History and clinical findings. Open Access Biology http://www.open-access-biology.com/legionella/edelstein.html〕 "Relative bradycardia" may also be present, which is low or low-normal heart rate despite the presence of a fever. Laboratory tests may show that kidney functions, liver functions and electrolyte levels are abnormal, which may include low sodium in the blood. Chest X-rays often show pneumonia with consolidation in the bottom portion of both lungs. It is difficult to distinguish Legionnaires' disease from other types of pneumonia by symptoms or radiologic findings alone; other tests are required for definitive diagnosis. Persons with Pontiac fever experience fever and muscle aches without pneumonia. They generally recover in two to five days without treatment. For Pontiac fever the time between exposure and symptoms is generally a few hours to two days. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Legionnaires' disease」の詳細全文を読む スポンサード リンク
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