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People can catch legionnaires’ disease by inhaling small droplets of water, suspended in the air, containing the bacteria. Certain conditions increase the risk from legionella, including:

  • water temperature between 20–45 °C, which is suitable for growth

  • a source of nutrients for the organism e.g. presence of sludge, scale or fouling

  • stored and/or re-cirulated water

  • creating and spreading breathable droplets of water, e.g. aerosol created by a cooling tower, or water outlets