Educational Content: This article is for informational purposes only and does not constitute medical advice. Always consult a healthcare provider for diagnosis and treatment.

Definition of Disease, Legionnaire

Medically reviewed by Dr. Otari Nergadze, Neurosurgeon | Updated: January 2026

Disease, Legionnaire: A disease due to the bacteria Legionella pneumophila found in plumbing, shower heads, water-storage tanks and air cooling systems. 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.

Legionnaire disease can cause a massive pneumonia associated with collapse of the respiratory function. It can be an overwhelming and sometimes fatal illness.

The disease was first identified as a sequel of the 1976 convention of the American Legion in some of those who had attended the convention. It was therefore named Legionnaire disease.

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