British Dictionary definitions for legionnaires' disease
a serious, sometimes fatal, infection, caused by the bacterium Legionella pneumophila, which has symptoms similar to those of pneumonia: believed to be spread by inhalation of contaminated water vapour from showers and air-conditioning plants
C20: after the outbreak at a meeting of the American Legion at Philadelphia in 1976
Legionnaires' disease Le·gion·naires' disease (lē'jə-nârz') n. An acute, sometimes fatal respiratory disease caused by Legionella pneumophila and characterized by severe pneumonia, headache, and a dry cough. Also called legionellosis.