Legionnaires’ disease

Legionella pneumophila is a bacterium of the genus Legionella, which causes legionnaires’ disease. This illness (which is also called legionella or legionellosis) can arise when people inhale the bacteria, such as in a(n) (emergency) shower, or from a sprinkler system or fire hose.

Preventing infection

EC Vastgoed regularly monitors the spray systems in the Hortus Botnaicus and the showers in Plexus and USC for possible contamination with Legionella. The cooling towers at the Sylvius Laboratory and the KOG building are also checked for possible contamination.

Report use of fire hoses, emergency showers and eye washes to your prevention officer or the AMD (Health and Safety department at the Faculty of Science). The AMD /prevention officer will direct those involved and bystanders to report to their (occupational) physician if they develop any symptoms.

Infection can be prevented by:

  • keeping the temperature of the water either below 20°C or above 65°C;
  • regularly flushing water through the pipes or tank;
  • not allowing mist or droplets (aerosols) to form as a result of turbulent water movement.

If it is not possible to take the measures listed above, disinfection is also possible with a sufficient amount of chlorine (at least 2% bleach in the ultimate concentration). In places where a potential risk persists, specific additional measures may be necessary.

What is Legionella pneumophila?

Species of Legionella can usually be found in low concentrations in watery environments and in moist soil. Under certain favourable circumstances the bacteria can multiply greatly in number. Still water with a temperature between 20° and 55°C and the presence of a biofilm (layer of slime) or other organic material are the ideal conditions for rapid reproduction. In this connection, contaminated systems (algae, rust, etc.) pose an extra risk, because there is relatively more still water in these conditions. Someone can become infected by inhaling this contaminated mist. The bacteria dies at a water temperature above 65°C.


Infection with Legionella pneumophila can only occur through the respiratory system. So, the infected water must in the form of aerosols (spray, mist, droplets). One can only become infected with Legionella pneumophila by way of the respiratory system. It is the inhalation of Legionella contained in water droplets (aerosols) that causes infection. The bacteria causes pneumonia (inflammation of the lungs) or flu-like symptoms. One cannot become infected by drinking contaminated water!

Legionella can be present in:

  • hot water pipes
  • cold water pipes which become heated by adjacent hot water pipes  
  • (extinguisher) showers (shower head)  
  • eye wash bottles
  • sprinkler systems  
  • spray systems in greenhouses and growing rooms
  • air humidifiers
  • air conditioners  
  • boilers  
  • cooling towers
  • and so-called ‘dead ends’ in the plumbing

Last Modified: 29-09-2014