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Legionnaires' disease (LEE-juh-nares) is caused by a type of bacteria called Legionella. The Legionella bacteria are found naturally in the environment, usually in water. People get Legionnaires' disease when they breathe in a mist or vapor (small droplets of water in the air) containing the bacteria. Patients with Legionnaires' disease usually have fever, chills, and a cough, which may be dry or may produce sputum. Some patients also have muscle aches, headache, tiredness, loss of appetite, loss of coordination (ataxia), and occasionally diarrhea and vomiting. Confusion and impaired cognition may also occur, as can a so-called 'relative bradycardia', i.e. low or low normal heart rate despite the presence of a fever. Paired sera (blood specimens) that show a four-fold increase in antibody levels when drawn shortly after illness and several weeks following recovery, can also be used to confirm the diagnosis.