Legionella are bacteria belonging to the Legionella sp. genus that occur naturally in the environment, and especially in watery environments (fresh water and artificially created bodies of water). They can easily colonise water systems which provide the ideal conditions for development:
- stagnant water where there are other microorganisms able to provide the nutrients that their own metabolism cannot produce, as well as scale or corrosion (iron, zinc);
- water temperature between 25°C and 45°C, optimum 32 - 35°C.
Legionellosis
Legionella spreads through the air and via the inhalation of microdroplets of contaminated water (aerosols). Contamination in humans can cause:
- a benign illness with flu-like symptoms (Pontiac fever)
- a serious illness with pneumonia (legionellosis) which can result in death for vulnerable people. Legionellosis is, therefore, a notifiable disease.
The gravity of the infection depends on the number of microorganisms inhaled, the virulence of the bacterial strain and the state of the infected person’s immune system. Legionella pneumophila serogroup 1 is by far the most virulent strain.
The most common source of contamination is the shower.
Monitoring for Legionella
Throughout Europe, and in a large number of countries worldwide, regulations relating to monitoring for Legionella spp. require the bacteriological quality of the water to be checked in all washroom facilities where there are points-of-use at risk. Health and Safety Executive guidance HSG274 Part 2* requires regular monitoring and analysis of both the hot and cold water, and highlights the importance of the bacteriological risk and the correct choice of suitable equipment.
Source: HSG274 Legionnaire's disease Part 2: The control of legionella bacteria in hot and cold water systems, published by the Health and Safety Exceutive in 2014
Monitoring levels for Legionella spp.
Alert level | < 100 CFU/L |
Remedial action | > 100 and up to 1,000 CFU/L |
Unacceptable level | > 1,000 CFU/L |
CFU/L: Colony Forming Units/Litre
Point-of-use filters should be used primarily as a temporary measure until a permanent safe engineering solution is developed, although long-term use of such filters may be needed in some healthcare situations.
In the event of a positive test result for Legionella:
First of all, the user's risk of exposure must be identified. Installing anti-Legionella filters is the most effective response if one of the following occurs: widespread contamination; contamination levels above 100 CFU/L; the serotype has been identified; a case of legionellosis has been diagnosed; the users are vulnerable patients. Chemical or thermal shocks are also effective, but implementing either can be problematic and will be less effective if the cause of the proliferation is not identified.
Find out about our anti-Legionella solutions for Public Buildings.
