Legionnaire disease: A disease due to the bacteria Legionella pneumophila found in plumbing, shower heads and water-storage tanks. Outbreaks of Legionella pneumonia have been attributed to evaporative condensers and cooling towers. The bacteria thrives in the mist sprayed from air-conditioning ducts and so it can infest an entire building or airplane. Travelers are especially vulnerable in the closed space within a plane.
Home hot water pipes have also been found to be a common source of the disease. The bacteria flourish at temperatures between 90 and 105 degrees and so can grow in the slimy gunk lining residential hot water pipes. People contract the bacteria by inhaling drops of water while showering, washing or even drinking.
The disease was first identified as a sequel of the 1976 convention of the American Legion in some of the Legionnaires who had attended the convention. It was therefore named Legionnaire disease.