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Legionella facts
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- Legionella was first discovered in 1976.
- It is normally contracted by inhaling tiny water droplets (aerosols) or ingestion
of contaminated water.
- The incubation period is between 2-10 days, but normally 3-6 days.
- People who do not develop full blown Legionella may have mild flu like symptoms.
- To date there are approximately 40 known species of L.pneumophila. Serogroup 1 is
the most common form of Legionella bacteria found in the UK.
- Legionella favours growth between 20 – 45°C.
- Legionella bacteria does not multiply in temperatures of less than 20°C and will
not survive above 60°C.
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- At 37°C the Legionella bacteria is at its most virulent.
- Conditions such as sediment, sludge and scaling are also favourable for incubation.
- Common places for growth of Legionella bacteria are in hot & cold water systems,
water storage and cooling towers.
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Guidance on the control of Legionella in water systems
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Water supply (water quality) regulations permit water suppliers to provide water
up to 25°C. However in winter this is normally 5-10°C. In prolonged summer conditions
water temperature can rise over 20°C. This needs to be monitored and action taken.
The temperature in a standard cold water system should be less than 20°C after
running the tap for 2 minutes. For thermal disinfection, the water temperature should
be brought up to 60°C every 3 days.
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The temperature in a standard hot water system should not be less than 50°C after
running the tap for 1 minute. All water systems should be routinely checked for
the correct temperature. To comply all the inspections and measurements should be
recorded and kept for up to 5 years.
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