What Is Legionella, and How Do People Get Legionnaires’ Disease?

Legionella is a type of bacteria. The CDC says it causes Legionnaires’ disease, a type of serious pneumonia, and Pontiac fever, a milder illness without pneumonia.

People get sick by breathing it in. The CDC says water containing Legionella can spread in droplets small enough to breathe in, that inhaling those droplets is the most common way people get sick, and that in general Legionnaires’ disease is not spread person to person. It says the bacteria become a health concern when they grow and spread in human-made building water systems such as showerheads and sink faucets, hot tubs, decorative fountains and water features, large complex plumbing systems and cooling towers.

The CDC says most healthy people exposed to Legionella do not get sick, and that people at increased risk include current or former smokers, people 50 years or older, and people with specific health issues or conditions.

Sources checked September 15, 2026. Every point below links the page it came from.

The sources behind this answer

  • Government sourceThe CDC says Legionnaires’ disease is a type of serious pneumonia caused by a type of bacteria called Legionella. CDC ↗
  • Government sourceThe CDC says Pontiac fever is a mild illness without pneumonia caused by Legionella bacteria. CDC ↗
  • Government sourceThe CDC says water containing Legionella can spread in droplets small enough to breathe in, and that inhaling those droplets is the most common way people get sick. CDC ↗
  • Government sourceThe CDC says people get Legionnaires’ disease by breathing in mist containing Legionella, and that in general it is not spread person to person. CDC ↗
  • Government sourceThe CDC says Legionella becomes a health concern when it grows in building water systems such as showerheads and faucets, hot tubs, decorative fountains, large complex plumbing systems and cooling towers. CDC ↗
  • Government sourceThe CDC says most healthy people exposed to Legionella do not get sick, and that current or former smokers, people 50 or older and people with specific health conditions are at increased risk. CDC ↗

Sources checked September 15, 2026. A brand statement is the company’s own claim, which we report but have not verified. Our grades are model-based estimates, not lab tests.

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