Legionellosis can present as two types of illness: Legionnaires’ (LEE-juh-nares) disease and Pontiac fever. The two illnesses can be diagnosed with similar tests, but are treated differently.
Legionnaires’ disease is a serious type of pneumonia (lung infection) frequently requiring hospitalization, whereas Pontiac fever is a less serious illness that is self-limiting and does not require treatment. People can get sick with Legionnaire's disease or Pontiac fever when they breathe in mist or accidently swallow water into the lungs containing Legionella (LEE-juh-nell-a) bacteria.
Legionnaire's Disease And Water Management Resources