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Causes & Transmission

Legionella in the Environment

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. The bacteria grow best in warm water, like the kind found in

  • Hot tubs
  • Cooling towers
  • Hot water tanks
  • Large plumbing systems
  • Decorative fountains

They do not seem to grow in car or window air-conditioners.

 

Spread of Disease

People get Legionnaires' disease when they breathe in a mist or vapor (small droplets of water in the air) containing the bacteria. One example might be from breathing in droplets sprayed from a hot tub that has not been properly cleaned and disinfected. The bacteria are not spread from one person to another person.

 

Man in hot tub

The bacteria are NOT spread from one person to another person.

Exposure

Most people exposed to the bacteria do not become ill. If you have reason to believe you were exposed to the bacteria, talk to your doctor or local health department. Be sure to mention if you have traveled in the last two weeks.

A person diagnosed with Legionnaires' disease in the workplace is not a threat to others who share office space or other areas with him or her. However, if you believe that your workplace was the source of the person's illness, contact your local health department.


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