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Legionnaires' (LEE-juh-nares) disease is caused by a type of bacterium called Legionella (LEE-juh-nell-a). The bacterium is named after a 1976 outbreak, during which some people who went to a Philadelphia convention of the American Legion suffered from a new type of pneumonia (lung infection) that became known as Legionnaires’ disease. A milder infection, also caused by Legionella, is called Pontiac fever. The term "legionellosis" (LEE-juh-nuh-low-sis) may be used to refer to either Legionnaires' disease or Pontiac fever.

Outbreak Investigation Tools

CDC has developed a number of resources to help health departments investigate legionellosis outbreaks.


Environmental Investigation Videos

clinicians taking water samplesCDC has developed six instructional videos on various environmental aspects of legionellosis outbreak investigations.


ELITE Program

CDC's ELITE Program

The Environmental Legionella Isolation Techniques Evaluation (ELITE) Program was created as a way for laboratories to test their Legionella isolation techniques against standardized samples.