Our Health Library information does not replace the advice of a doctor. Please be advised that this information is made available to assist our patients to learn more about their health. Our providers may not see and/or treat all topics found herein.

Legionnaires' disease

Legionnaires' disease is an infection of the lungs (pneumonia) caused by a type of bacteria called Legionella pneumophila.

People develop Legionnaires' disease from breathing in the bacteria, which may be carried in airborne water droplets from contaminated water sources, such as air-conditioning cooling towers, plumbing systems, hot water tanks, and spas. These sources often have warm, stagnant water that allows bacteria to grow. People who work near natural bodies of water do not appear to be at risk.

Legionnaires' disease is not passed from one person to another. It usually occurs in single, isolated cases or in groups of people who are exposed to the same source of infection. Most cases of Legionnaires' disease affect people older than 50 or people whose immune systems are weakened by other diseases or by smoking.