Legionnaires' Disease Fact Sheet

PDF Version of this Fact Sheet

What is Legionnaires' disease?

Legionnaires’ disease is a serious type of pneumonia (lung infection) caused by Legionella bacteria. 

Common Source of Infection

Legionella can be found naturally in freshwater environments (like lakes and streams), but generally only becomes a health concern when it grows and spreads in manmade plumbing structures (e.g., cooling towers, hot tubs, building water systems).​


The Legionella bacterium is spread by the release of small droplets of contaminated water into the air from air conditioning cooling towers, showers, misters, humidifiers, etc. To cause illness, infected water droplets must be inhaled (breathed in) by a susceptible person. Generally, the disease is not spread from person to person.

Signs & Symptoms 

  • Cough
  • Shortness of breath
  • Fever
  • Muscle aches
  • Headache
  • Diarrhea
  • Nausea
  • Confusion

Risk Factors

Most healthy people exposed to Legionella do not get sick.  People at increased risk of getting sick are:


·        People 50 years or older

·        Current or former smokers

·        People with cancer or underlying illnesses such as chronic lung disease (like COPD or emphysema), diabetes, liver disease, or kidney disease

·        People with weak immune systems or who take drugs that weaken the immune system (like after a transplant operation or chemotherapy)


Legionnaires’ disease is treated with commonly available antibiotics.​

If you think that you might have Legionnaires' disease, contact your primary care provider immediately.