About Legionnaires' Disease

Key points

  • Legionnaires' disease is a serious type of pneumonia caused by Legionella bacteria.
  • Certain people are at increased risk for this infection, but it's treatable with antibiotics.
  • People can get Legionnaires' disease by breathing in mist containing Legionella bacteria.
  • To prevent Legionnaires' disease, reduce the risk of Legionella growth and spread.
An older man coughing

What it is

Legionnaires' disease is a type of serious pneumonia caused by a type of bacteria called Legionella.


Legionella most commonly causes one of two lung diseases:

  • Legionnaires' disease is a type of severe pneumonia
  • Pontiac fever is mild respiratory disease

Rarely, Legionella can cause infections outside of the lungs, such as heart or wound infections.

Keep Reading: About Pontiac Fever


It usually stakes 2 to 14 days after being exposed to Legionella bacteria to develop Legionnaires' disease symptoms. However, it can take longer.

Symptoms of Legionnaires' disease are similar to other types of pneumonia.

Symptoms include:

  • Cough
  • Fever
  • Headaches
  • Muscle aches
  • Shortness of breath

Other symptoms, such as confusion, diarrhea, or nausea can also occur.

Risk factors

Most healthy people exposed to Legionella don't get sick. However, certain factors put people at increased risk for getting Legionnaires' disease.

Keep Reading: Risk Factors


A type of bacteria called Legionella causes Legionnaires' disease. People can get Legionnaires' disease when they breathe in mist that contains the bacteria.

Keep Reading: Causes and Spread


The key to preventing Legionnaires' disease is to reduce the risk of Legionella growth and spread.

In buildings and public hot tubs

Building owners and managers can use a water management program to help control Legionella.

At home

There are steps people can take to help protect themselves from waterborne germs in their home.

In motor vehicles

Legionella can grow in the windshield wiper fluid tank of a vehicle, particularly if the tank is filled with water. To prevent growth and spread of Legionella, only use genuine windshield cleaner fluid and follow the vehicle manufacturer recommendations, if available.

Testing and diagnosis

A chest x-ray can confirm if someone has pneumonia. Other tests are needed to see if Legionella is causing a patient's pneumonia:

  • Urine test
  • Laboratory test that involves taking one of the following samples:
    • Sputum (phlegm)
    • Washing from the lung

Treatment and recovery

Legionnaires' disease requires treatment with antibiotics. Most cases of this illness can be treated successfully. Identifying and treating the illness early can increase the chances of getting better.

Healthy people usually get better after being sick with Legionnaires' disease, but they often need care in a hospital.


Possible complications of Legionnaires' disease include:

  • Lung failure
  • Death

About 1 out of every 10 people who gets sick with Legionnaires' disease will die due to complications from their illness. For those who get Legionnaires' disease during a stay in a healthcare facility, about 1 out of every 4 will die.


Legionella was discovered after an outbreak in 1976 among people who went to a Philadelphia convention of the American Legion. Those who were affected suffered from a type of pneumonia that eventually became known as Legionnaires' disease.


General resources

Fact sheet: Legionnaires' disease

Infographic: How Legionella affects building water systems and people

For professionals

How to control Legionella
For building owners and managers

How to investigate Legionella cases
For public health professionals