Legionella Risk

Legionella are a range of bacteria widespread in natural fresh water which can if they proliferate cause Legionnaires’ disease or Legionellosis - potentially fatal forms of pneumonia. In the UK there are between 200 and 300 cases per year of which approximately 30 are fatal.


While the ecology of Legionella in water systems is not fully understood, in the laboratory, it will grow optimally in stagnant nutrient rich water in the temperature range 20°C to 45°C (37°C body temperature) and pH 6.5-7.5. Water contaminated by Legionella only presents a risk when it is dispersed in air in the form of an aerosol (very fine water droplets / spray) such as that from a shower. Legionnaires’ disease can therefore be contracted where there are opportunities to inhale infected water droplets.



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