How to reduce the risk of Legionella after a summer break?

Empty classrooms, closed dental practices, construction sites or other businesses look abandoned. Besides staff enjoying their well-deserved holiday, these places have one thing in common: they are the ideal breeding grounds for the Legionella bacteria. It is a lethal pathogen, when untreated, as it causes legionellosis, an infectious disease that severely affects the lungs.  

The bacterium thrives in humid conditions with a temperature between 25 °C and 55 °C.
For example, a shower room, cooling towers or air handling unit with a humidifier. Haven’t used these for a while? Then the Legionella bacteria can settle and multiply in the stagnant water.
 

Drinking water contaminated with Legionella will not infect you. However, you can get infected if you breathe in contaminated water particles, also known as aerosol particles. This may happen when water is atomised, for example, when sprayed. The bacteria cannot be transmitted from person to person. 

Once infected, the bacteria can cause Legionnaires’ disease, a serious lung disease that can lead to chronic illness or death if not treated early. A milder course of disease also exists: Legionella flu.

Every company is required by law to draw up and perform a risk analysis that evaluates the hazards due to the development of Legionella bacteria. The results are used to draw up a management plan.

You use the preventive measures to start up safely after the summer break: 

• Flush cold water taps and pipes thoroughly with cold water (< 20 °C) for at least 5 minutes. 

You must avoid water splashing. For example, place a sponge under the water stream, disassemble shower heads before flushing, etc. If you cannot remove a shower head, wrap it with a plastic bag and make a single opening.

• Turn up boilers, instantaneous water heaters and hot water production appliances as high as possible (+ 60 °C) to carry out thermal disinfection. This means that you first open the tap furthest away from the boiler and then progressively the other taps. You then ensure each water point is ‘treated’ with a high enough temperature. 
   
  • Make sure you check that the taps used for mixing water temperatures are set as high as possible. 
  • To be absolutely certain, measure the temperature at each tap point. Because the actual temperature may differ from the ‘set’ temperature. The length of time to flush the water depends on the temperature measured at the tap point: 5 minutes at 70 °C and 10 minutes at 65 °C. 
  • To prevent the risk of scalding, you should carry out the thermal disinfection at a time when no one is using the taps and flush the appliances with cold water after disinfection.
  • Make sure everyone knows when the disinfection will take place.
  • Also, always check that the pipes can withstand high temperatures. If not, it may cause warping, cracking or speed up corrosion.