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CDC Legionella toolkit

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DEVELOPING A LEGIONELLA WATER MANAGEMENT PROGRAM 5 Factors internal to buildings that can lead to Legionella growth 6 6 6 6 6 6 6 Biofilm: Protects Legionella from heat and disinfectant; provides food and shelter to germs; grows on any surface that is constantly moist and can last for decades Scale and sediment: Uses up disinfectant and creates a protected home for Legionella and other germs Water temperature fluctuations: Provide conditions where Legionella grows best (77°F–108°F); Legionella can still grow outside this range Water pressure changes: Can cause biofilm to dislodge, colonizing downstream devices pH: Disinfectants are most effective within a narrow range (approximately 6.5 to 8.5) Many things can cause the hot water temperature to drop into the range where Legionella can grow, including low settings on water heaters, heat loss as water travels through long pipes away from the heat source, mixing cold and hot water within the plumbing system, heat transfer (when cold and hot water pipes are too close together), or heat loss due to water stagnation. In hot weather, cold water in pipes can heat up into this range. Inadequate disinfectant: Does not kill or inactivate Legionella. Even if the water entering your building is of high quality, it may contain Legionella. In some buildings, processes such as heating, storing, and filtering can degrade the quality of the water. These processes use up the disinfectant the water entered with, allowing the few Legionella that entered to grow into a large number if not controlled. Water stagnation: Encourages biofilm growth and reduces temperature and levels of disinfectant. Common issues that contribute to water stagnation include renovations that lead to 'dead legs' and reduced building occupancy, which can occur in hotels during off-peak seasons, for example. Stagnation can also occur when fixtures go unused, like a rarely used shower in a hospital room.

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