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Legionnaires' disease is caused by a type of bacteria called Legionella. The bacteria got its name in 1976, when many people who went to a Philadelphia convention of the American Legion suffered from an outbreak of this disease, a type of pneumonia (lung infection). Although this type of bacteria was around before1976, more illness from Legionnaires' disease is being detected now. This is because we are now looking for this disease whenever a patient has pneumonia.
Each year, between 8,000 and 18,000 people are hospitalized with Legionnaires' disease in the U.S. However, many infections are not diagnosed or reported, so this number may be higher. More illness is usually found in the summer and early fall, but it can happen any time of year.
People get Legionnaires' disease when they breathe in a mist or vapor (small droplets of water in the air) that has been contaminated with the bacteria. One example might be from breathing in the steam from a whirlpool spa that has not been properly cleaned and disinfected.
The bacteria are NOT spread from one person to another person.
Legionnaires' disease can have symptoms like many other forms of pneumonia, so it can be hard to diagnose at first. Signs of the disease can include: a high fever, chills, and a cough. Some people may also suffer from muscle aches and headaches. These symptoms usually begin 2 to 14 days after being exposed to the bacteria.
A milder infection caused by the same type of Legionella bacteria is called Pontiac Fever . The symptoms of Pontiac Fever usually last for 2 to 5 days and may also include fever, headaches, and muscle aches; however, there is no pneumonia. Symptoms go away on their own without treatment and without causing further problems.
Pontiac Fever and Legionnaires' disease may also be called "Legionellosis" separately or together.
Most people with Legionnaires’ disease will have pneumonia (lung infection) since the Legionella bacteria grow and thrive in the lungs. Pneumonia is confirmed either by chest x-ray or clinical diagnosis. Several laboratory tests can be used to detect the Legionella bacteria within the body. The most commonly used laboratory test for diagnosis is the urinary antigen test, which detects Legionella bacteria from a urine specimen, or sample. If the patient has pneumonia and the test is positive, then the patient is considered to have Legionnaires’ disease. Additionally, if the Legionella bacteria are cultured (isolated and grown on a special media) from a lung biopsy specimen, respiratory secretions, or various other sites, the diagnosis of Legionnaires’ disease is also considered confirmed. Finally, paired sera (blood specimens) that show a specific increase in antibody levels when drawn shortly after illness and several weeks following recovery, can also be used to confirm the diagnosis.
Legionnaires' disease can be very serious and can cause death in up to 5% to 30% of cases. Most cases can be treated successfully with antibiotics [drugs that kill bacteria in the body], and healthy people usually recover from infection.