What is legionella?

Legionella bacteria are responsible for causing a family of diseases collectively known as Legionellosis . This family includes Pontiac fever and Lochagoilhead fever. But the most serious by far is Legionnaires’ disease, which if untreated can be fatal.

While everyone is susceptible to infection, you are at a higher risk if you:

 

  • Are aged over 45
  • Smoke or drink heavily
  • Suffer from chronic respiratory or kidney disease
  • Have been diagnosed with type 2 diabetes
  • Have an impaired immune system

Where Legionella thrive

Legionella bacteria thrive in airborne water droplets. Small populations are commonly present in rivers, lakes and reservoirs. The bad news is that Legionella are also found in man-made water systems common in everyday urban and working environments such as cooling towers, evaporative condensers, hot and cold-water systems, and spa pools.

However, the news is not all bad. Legionella only flourishes if:

  • The water temperature is 20-45°C
  • Water droplets are dispersed as they form (e.g. aerosol in a cooling tower or water outlets)
  • The droplets have been formed from water that has been stored and/or recirculated
  • The water container has deposits such as rust, scale or biofilms which support bacterial growth

This means that outbreaks of Legionella can largely be prevented by:

  • Maintaining temperatures above 50°C for hot water and below 20°C for cold waterwater
  • Preventing stagnant proximity or dead legs/dead ends in pipe insulation
  • Installing point-of-use filters, especially where higher risk groups of people are present such as hospitals
  • Copper and silver ionization treatments

For new builds, architects and engineers can design Legionella prevention into their buildings by:

  • Keeping pipework short and direct
  • Insulating piping and tanks
  • Using materials that discourage the growth of Legionella
  • Fitting tanks with lids and insect screens to prevent contamination and dissemination

It is important to note that health authorities advise against reliance on environmental monitoring. Studies have shown that testing is erratic, too often producing a negative result when there is no legionella present. Instead, authorities recommend focusing on the management of appropriate control measures – and designing for clean-air buildings.