The scourge of ‘Legionella’

The Columbus Dispatch  • 
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Centers for Disease Control and Prevention
Legionella pneumophilia bacteria, seen in this colorized 8000X electron micrograph image, occur naturally in the environment, usually in water.

Some facts about the bacterium that causes Legionnaires’ disease:


Legionella pneumophilia is found naturally in the environment, usually in water. The bacteria grow best in warm water, such as that found in hot tubs, hot-water tanks, decorative fountains, large plumbing systems and air-conditioning cooling towers in large buildings.

Spread of the disease

People come in contact with the bacteria when they breathe in small droplets of water in the air, such as during a shower. The bacteria thrive in the lungs but are not spread from person to person.

Exposure and symptoms

Most people exposed to Legionella do not become ill. Symptoms include cough, shortness of breath, high fever, muscle aches and headaches.


Between 8,000 and 18,000 people are hospitalized with Legionnaires’ in the United States each year, mainly in the summer and early fall. However, many infections are not diagnosed or reported.

Most at risk

Smokers or people who are older than 50 or have chronic lung disease or a weakened immune system.


Most people get well after taking antibiotics. But the disease can cause lung failure leading to death in 5 percent to 30 percent of cases.


Proper maintenance of water systems, including appropriate temperatures and disinfectants. Hot tubs are particularly challenging, and at-risk people might want to avoid them.


The first documented outbreak of the disease was at a 1976 Philadelphia convention of the American Legion, hence the name. Of 221 cases, 34 people died.

Sources: Centers for Disease Control and Prevention, The New York Times