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06/11/24 Public Health Education Topic: Legionellosis

Per CDC:


  • Legionella bacteria cause Legionnaires' disease and Pontiac fever.

  • Water systems and devices can spread Legionella to people.

  • The most common way for someone to get sick is by breathing in mist containing Legionella.

How it spreads

Once Legionella grows and multiplies in a building water system, it can spread to people in a few ways.

Breathing in mist:

Water containing Legionella can spread in droplets small enough for people to breathe in. People can get Legionnaires' disease or Pontiac fever when they breathe in (inhale) those small droplets containing the bacteria. This is the most common way people get sick.

Swallowing water into the lungs:

Less commonly, people can get sick by aspiration of drinking water containing Legionella. This happens when water accidently goes into the lungs while drinking. People at increased risk of aspiration include those with swallowing difficulties.

Legionnaires' Disease informational pdf: Legionnaires’ Disease (



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