Health Topic

Legionnaires' Disease

Legionnaires' Disease (Legionella Pneumonia) is caused by bacteria. You get it by breathing in mist from water that contains the bacteria. Learn more.

Reviewed Reviewed by a registered pharmacistGeneral information

Also called: Legionellosis

Important: This page is general information, not medical advice. It does not recommend or prescribe any treatment. Always consult your doctor or pharmacist before starting, stopping or changing any medicine.

About Legionnaires' Disease

Legionnaires' disease is a serious type of pneumonia caused by Legionella bacteria. The disease got its name when a group of people at an American Legion convention became ill with this type of pneumonia.

Legionella is found naturally in freshwater, such as lakes and rivers. It can also be found in soil. But people usually only get sick from it when if it grows and spreads in man-made water systems. These systems can include hot tubs, fountains, and the plumbing systems of large buildings, such as hotels or nursing homes.

Legionella can also cause Pontiac fever. This is a milder, flu-like illness that doesn't infect your lungs.

You usually can't get infected by drinking water that contains the bacteria unless you aspirate it (accidentally breathe the water into your lungs). The bacteria don't spread from person to person. Disease outbreaks happen when many people are exposed to the same water source that contains the bacteria.

Most healthy people who come in contact with the bacteria do not become sick. You are more likely to develop an infection if you:

  • Are over the age of 50
  • Are a current or former smoker
  • Have a chronic (long-lasting) disease such as diabetes or kidney failure
  • Have a chronic lung disease such as COPD or emphysema
  • Have a weakened immune system due to a disease such as HIV or cancer or are taking medicines that suppress your immune system
  • Live in a long-term care facility
  • Have recently stayed in a hospital or had surgery requiring anesthesia

The symptoms usually show up 2 to 14 days after you were exposed to Legionella bacteria. Most of the symptoms are similar to those of other types of pneumonia. But Legionnaires' disease may also cause gastrointestinal symptoms and mental changes.

The symptoms of Legionnaires' disease may include:

  • Cough
  • High fever
  • Chills
  • Headache
  • Chest pain
  • Shortness of breath
  • Fatigue
  • Nausea and vomiting
  • Diarrhea
  • Confusion

Legionnaires' disease can cause life-threatening complications such as respiratory failure, kidney failure, and sepsis.

About 1 out of every 10 people who get sick with Legionnaires' disease will die from complications of the illness.

To find out if you have Legionnaires' disease, your health care provider will probably order a chest x-ray to see if you have pneumonia. If you do have it, lab tests such as a urine or sputum test can check for the Legionella bacteria. Your provider may also order a blood test to see if you have been exposed to the bacteria.

If you have Legionnaires' disease, you will likely need care in a hospital. The treatment is with antibiotics. Most people will recover, especially if they were healthy when they got the disease. Getting treatment early can increase the chances of getting better.

You can lower your risk of getting Legionnaires' disease if you:

  • Clean all your water-related devices regularly. This could include portable humidifiers, water heaters, air conditioners, and nasal rinses.
  • If you haven't used your faucets and showerheads for a week or more, flush them by letting the hot and cold faucets run for at least two minutes before use.
  • Avoid exposure to water sources such as decorative foundations or hot tubs if you don't know how well they are maintained.
  • Use windshield cleaner in your wiper fluid tank in your car instead of water.
  • Ask about how well your buildings' water systems are maintained.

Centers for Disease Control and Prevention

It sits within Infections and Lungs and Breathing.

The lead U.S. institute for this subject is the National Institute of Allergy and Infectious Diseases.

When to speak to someone. Reading about a topic cannot tell you whether it applies to you. Speak to a doctor or pharmacist if symptoms are severe, sudden, getting worse, or simply not going away — and seek emergency care immediately for chest pain, breathing difficulty, sudden weakness or confusion, or a serious allergic reaction.

Research on Legionnaires' Disease

9 studies areregistered for this condition on ClinicalTrials.gov, the U.S. National Library of Medicine's public registry. A selection is below — the links go straight to the registry entry, not to a summary of ours.

What a registered study does and does not mean. Registration means a study exists and has been declared publicly. It says nothing about whether the treatment being tested works, is safe, or is available to you. Many studies find no benefit — that is what research is for. Never seek out an experimental treatment on the strength of a registry entry alone.

Research currently under way

Research already completed

Study data from ClinicalTrials.gov, a service of the U.S. National Library of Medicine. Retrieved 2026-07-30. Registry entries are supplied by study sponsors and investigators; ClinicalTrials.gov does not verify their scientific validity. PocketsInfo is not affiliated with, and not endorsed by, the NLM or the NIH.

Where to read more

Rather than paraphrase, we point you to the primary sources. Every link below is to a government health agency, a national institute or a recognised medical body — grouped by what you are trying to find out.

Learn More

Clinical Trials

Medical subject headings

Clinicians and researchers index this subject under Legionnaires' Disease. These are the terms to use when searching medical literature.

This page is built from the MedlinePlus health topic record for Legionnaires' Disease, a service of the U.S. National Library of Medicine (NLM), National Institutes of Health. Information is from MedlinePlus.gov. PocketsInfo is not affiliated with, and is not endorsed by, the NLM or the NIH. Retrieved 30 July 2026.