An outbreak of this disease in Philadelphia in 1976, largely among people attending a state convention of the American Legion, led to the name “Legionnaires’disease.” Legionnaires’ disease is a pneumonia (lung infection) and you can catch it by inhaling droplets of water contaminated with Legionella. The bacteria can be dispersed from the water, where it lives, to the air through aerosols from things like showers, air conditioning or hot tubs. It can be found in both natural and man-made water systems. The bacteria can live and multiply in water at temperatures of 25°C (77°F) to 50ºC (122ºF).