Legionella

Legionella bacteria can be the cause of two illnesses in humans: Legionnaires’ disease, an infection that produces pneumonia and Pontiac fever, which resembles acute influenza. When designing air conditioning systems, how to reduce the risk of bacteria growth must be considered.

The Legionella bacteria is common in wet and humid environments. The optimal temperature range at which the bacteria form is 35–46ºC, and thus they typically thrive in water that has a temperature of 30–50ºC.

There are many different species of Legionella bacterium, and far from all of them cause sickness in humans. Legionella bacteria can be the cause of two illnesses in humans:
- Legionnaires’ disease, an infection that produces pneumonia
- Pontiac fever, which resembles acute influenza.

The bacteria must be inhaled. Infection occurs after inhaling a fine aerosol of contaminated water droplets. Typical sources of infection are cooling towers in large central air conditioning systems, whirlpools and showers.

Suspected source of transmission can be tested by taking water samples from the pipe system, taps, etc.
There are various hygienic methods of minimising the risk of the bacteria growth and of killing them:

  • disinfection, e.g. chlorine dioxide
  • heat treatment by circulating hot water
  • filter system
  • UV treatment




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