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Legionnaires’ disease is a severe type of pneumonia, or lung infection. Bacteria called Legionella cause this infection. The bacteria were discovered after an outbreak at a Philadelphia convention of the American Legion in 1976. Those who were affected developed a form of pneumonia that eventually became known as Legionnaires’ disease.
Legionella bacteria thrive in warm water. People become infected with Legionella by breathing in contaminated droplets of water in the air. Outbreaks have been linked to water systems in hospital buildings and to whirlpool spas in hotels and cruise ships.
Approximately 5,000 people are hospitalized in the United States each year with Legionnaires’ disease. However, the number of infections is probably higher, because many infections aren’t diagnosed or reported. Some cases are so mild that affected individuals never seek treatment.
Many people who are exposed to Legionella don’t become sick. When illness does occur, however, it’s important to see a doctor right away. Legionnaires’ disease is a serious, life-threatening illness that requires prompt treatment.
Legionella may also cause a milder condition referred to as Pontiac fever. Pontiac fever doesn’t cause pneumonia and isn’t life-threatening. It has symptoms similar to those of a mild flu, and it usually goes away on its own. Pontiac fever and Legionnaire’s disease are sometimes collectively called Legionellosis.
Legionnaires’ disease will usually start causing symptoms within 2 to 14 days after exposure to the bacteria. This period is called the incubation period. The symptoms of Legionnaires’ disease are similar to those of other types of pneumonia.
The most common symptoms include:
Other symptoms may include:
Bacteria called Legionella causes Legionnaires’ disease. The bacteria invade the lungs and cause an infection known as pneumonia.
Legionella usually live in warm freshwater. Common locations include:
The bacteria can survive outdoors, but they’re known to multiply rapidly in indoor water systems. People get infected by inhaling water droplets or mist in the air that’s contaminated with the bacteria. The disease can’t be spread directly from person to person.
Not everyone who breathes in contaminated air droplets will get sick. However, you’re at a higher risk for developing Legionnaires’ disease if you:
When Legionnaires’ disease goes untreated, life-threatening complications can develop. These include:
These complications can progress rapidly, especially in people who already have weakened immune systems.
Your doctor can diagnose Legionnaires’ disease by testing your blood or urine for the presence of Legionella antigens. Antigens are substances that your body recognizes as harmful. Your body produces an immune response to antigens to fight infection. Your doctor may also test a sample of sputum, or phlegm, for the Legionella bacteria.
Your doctor might also perform a chest X-ray. While the X-ray can’t be used to confirm Legionnaires’ disease, it can help determine the severity of your lung infection.
Legionnaires’ disease is always treated with antibiotics. Treatment is usually started as soon as the disease is suspected, without waiting for confirmation. Prompt treatment significantly lowers the risk of complications.
Many people completely recover with treatment, but most will need care in the hospital. Elderly people and those with other health conditions are particularly vulnerable to the effects of Legionnaires’ disease. While in the hospital, they may receive oxygen or other breathing support. They may also be given fluids and electrolytes through a vein in their arm (IV) to treat dehydration.
The outlook is typically good for healthy people who receive prompt treatment. However, the length of recovery time will depend on the severity of the disease and how quickly treatment is received. Faster treatment means better results.
Legionnaires’ disease is usually more serious in elderly people who have weakened immune systems or other medical conditions. If you’re elderly, you have a higher risk of developing complications and you may need to stay in the hospital for an extended period.
There’s no vaccine available for Legionnaires’ disease. However, it’s possible to prevent the disease by properly disinfecting and cleaning potential sources of the Legionella bacteria. Preventive measures include:
Avoiding smoking can also significantly lower your risk of infection. Smokers are much more likely to develop Legionnaires' disease if they’re exposed to Legionella bacteria.
Written by: Jacquelyn Cafasso
Medically reviewed on: Mar 23, 2017: Suzanne Falck, MD, FACP
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