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Legionella is a type of bacteria found naturally in the environment, usually in water. Legionella bacteria grow best in warm water like the kind found in hot tubs, cooling towers, hot water tanks, large plumbing systems and decorative fountains. They do not seem to grow in car or window air conditioners.

Legionella bacteria can make people sick when they breathe it in through contaminated mist or vapor (small droplets of water in the air). This can happen when you drink, shower or bathe in contaminated water. Legionella bacteria are NOT spread from person-to-person. Most people exposed to the bacteria do not become ill.

Legionnaires’ Disease

Breathing in Legionella bacteria can cause Legionnaires’ disease, a severe form of pneumonia (lung infection). Legionnaires’ disease can have symptoms like many other types of pneumonia and can be difficult to diagnose at first. Signs of Legionnaires’ disease include:

  • Cough
  • Shortness of breath
  • High fever
  • Muscle aches
  • Headache

These symptoms usually begin 2 to 14 days after being exposed to the Legionella bacteria. If you believe that you were exposed to Legionella and have these symptoms, please talk with your doctor. Legionnaires’ disease requires treatment with antibiotics and may require hospitalization.

Pontiac Fever

Breathing in Legionella bacteria also can cause a milder infection called Pontiac Fever. The flu-like symptoms are similar to those of Legionnaires’ disease, they usually last for 2 to 5 days and go away on their own without treatment. Pontiac Fever is not a type of pneumonia.

People at Higher Risk of Getting Sick

Most healthy individuals do not become infected with Legionella bacteria after exposure. People at higher risk of getting sick are:

  • Older people (usually 50 years of age or older)
  • Current or former smokers
  • Those with a chronic lung disease (like COPD or emphysema)
  • Those with a weak immune system from diseases like cancer, diabetes, or kidney failure
  • People who take drugs that suppress (weaken) the immune system (like after a transplant operation or chemotherapy)

Incidence of Legionnaires’ Disease

CDC estimates that between 8,000 and 18,000 people are hospitalized with Legionnaires' disease in the United States each year. However, only about 3,000 are reported to CDC.

Fixing the Problem

When Legionella bacteria are identified in a water system, CDC recommends that measures be taken to remove the bacteria from the water, a process called remediation. The most frequently used initial remediation measures include super-heating or super-chlorinating the water system. These methods do not usually lead to permanent removal of Legionella bacteria, so a long term-plan for preventing the growth of Legionella bacteria is almost always necessary.