Legionella are bacteria that are naturally found in freshwater sources such as lakes and streams. However,
Legionella bacteria can grow and spread in human-made water systems, such as hot tubs, cooling towers (which use water to cool air as part of centralized air conditioning systems for buildings or industrial processes), hot water tanks, decorative fountains, and large buildings with complex water systems. Small water droplets or mist from these sources can contain Legionella bacteria, which people can inhale, causing infection in the lungs. Infection with
Legionella (also called “legionellosis") can result in two different illnesses:
Legionnaires' disease (a serious form of pneumonia) or
Pontiac fever (a milder illness). Generally, Legionnaires' disease and Pontiac fever are
not spread from person to person. The best way to prevent legionellosis is to reduce exposure to water sources where Legionella grow.
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What is Legionnaires' disease?
Legionnaires' disease is a severe type of lung infection or pneumonia, which often requires hospitalization, though it can usually be treated successfully with antibiotics. Symptoms of Legionnaires' disease are similar to other types of pneumonia and include cough, shortness of breath, fever, chills, headaches, muscle aches, nausea, vomiting, diarrhea, and confusion.
People over the age of 50, current and former smokers, people with chronic lung disease, and people with weakened immune systems are at increased risk for Legionnaires' disease. Most healthy people exposed to
Legionella do not develop Legionnaires' disease.
What is Pontiac fever?
Pontiac fever is a milder, self-limiting infection, and symptoms can include fever and muscle aches. Symptoms of Pontiac fever usually get better in less than a week and do not require medical care.