Legionella is a gram-negative bacterium that is known to cause Legionellosis including a type of pneumonia illness called Legionnaires’ disease and a mild flu- like fever called Pontiac fever. In simple term, Legionnaires is a ling infection disease that one can get from inhaling droplets of water from taps and showers, spa pools, air conditioning, hot tubs, and humidifiers that are infested with legionella bacteria.