Legionella organisms can be found in many types of water systems. However, the bacteria reproduce to high numbers in warm, stagnant water (95 F-115 F), such as that which is found in certain plumbing systems and hot-water tanks, cooling towers, and evaporative condensers of large air-conditioning systems, and hot tubs. Cases of legionellosis have been identified throughout the United States and in several other countries. The disease likely occurs worldwide.The bacterium thrives in the mist aerosolized from air-conditioning ducts. Thus, it can infest an entire building or airplane. Factors that are now known to enhance the growth of Legionella bacteria in human-made water environments include the following:
Water temperatures of 77 F-107.6 F
Stagnation of the water
Scale and sediment in the water
Certain free-living amoebae organisms in water capable of supporting intracellular growth of Legionellae