Legionnaire's disease is a lung disease caused by infection with the bacterium Legionella pneumophilia. It takes its name from the serious outbreak that occurred during a convention of the American Legion held in Philadelphia in 1976. Identified the following year, the bacterium thrives in water and may be found in defective heating, ventilation, and air-conditioning systems. It is inhaled in fine water droplets present in the air. The disease is pneumonia-like in its effects and is treated with antibiotics.