Legionnaires Disease

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

Where Legionella Bacteria is Found

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, or parts of the air-conditioning systems of large buildings.

How People Get Legionnaires' Disease

People get Legionnaires' disease when they breathe in a mist or vapor (small droplets of water in the air) that has been contaminated with the bacteria. One example might be from breathing in the steam from a whirlpool spa that has not been properly cleaned and disinfected. Other infections have been linked to aerosol sources such as cooling towers (air-conditioning units from large buildings) and water used for drinking and bathing. The bacteria are NOT spread from one person to another person.

People Most at Risk

People most at risk of getting sick from the bacteria are older people (usually 65 years or older), people who smoke or have chronic lung disease (like emphysema), and those who have weak immune systems from cancer, diabetes, kidney failure, medications, or other medical conditions.

Protect You and Your Family

There are no vaccines that can prevent Legionnaires' disease.

Instead, the key to preventing Legionnaires' disease is to make sure that building owners and managers maintain building water systems in order to reduce the risk of Legionella growth and spread. Examples of building water systems that might grow and spread Legionella include:

  • Hot tubs
  • Hot water tanks and heaters
  • Large plumbing systems
  • Cooling towers (structures that contain water and a fan as part of centralized air cooling systems for building or industrial processes)
  • Decorative fountains

CDC Toolkit: Developing a Legionella Water Management Program helps building owners and managers develop and implement a water management program to reduce their building's risk for growing and spreading Legionella.

For residential homes, see Preventing Waterborne Germs at Home, CDC.

Symptoms of Legionnaires' Disease

  • Symptoms usually begin 2 to 10 days after being exposed to the bacteria.
  • Legionnaires' disease can have symptoms like many other types of pneumonia, so it can be hard to diagnose at first. Signs of the disease can include a high fever, chills, and a cough. Some people also have muscle aches or headaches.
  • A milder infection caused by the same type of Legionella bacteria is called Pontiac Fever. The symptoms of Pontiac Fever usually last for 2 to 5 days and may also include fever, headaches, and muscle aches; however, there is no pneumonia. Symptoms go away on their own without treatment and without causing further problems.
  • Pontiac Fever and Legionnaires' disease are also called “Legionellosis.”

Legionnaires' disease can be very serious and can be fatal in 5 percent to 30 percent of cases.

Diagnosis and Treatment

Most people with Legionnaires' disease get pneumonia (lung infection) since the Legionella bacteria grow and thrive in the lungs. Pneumonia is confirmed either by chest x-ray or clinical diagnosis. Several laboratory tests can be used to detect the Legionella bacteria in the body. CDC recommends that clinicians collect both a urine specimen (for a urine antigen test) as well as a lower respiratory tract specimen such as sputum for bacterial culture or PCR (polymerase chain reaction).

Most people can be treated successfully with specific antibiotics (drugs that kill bacteria in the body).

More Resources

For the Water Systems

For Health Care and Local Health Partners

Notifiable Condition: Report Legionellosis