Legionellosis is an infectious disease caused by Gram-negative,
aerobic bacteria belonging to the genus Legionella. More
than 90 % of pneumonic legionellosis (Legionnaires’ disease)
cases are caused by Legionella pneumophila, an organism that
multiplies in water at temperatures between 25 ºC and 45 ºC.
Danish surveillance studies show that serogroup 1 accounts
for 60 % and serogroup 3 accounts for 20 % of Legionnaires’
disease cases.
Legionnaires’ disease can be a rather severe disease with
massive pneumonia and organ failures, but there is also a
range of cases with a milder flue-like illness, often called
Pontiac fever.