Legionella

The legionella bacterium is a common species found in natural water bodies such as lakes and rivers as well as in man-made water systems used in domestic, commercial and industrial properties. In normal conditions, it poses very little problem for humans but favourable conditions will encourage its growth which in turn increases the risk of inhaling the bacteria and suffering from resultant Legionnaires’ disease (Legionellosis).

Employers and landlords have a legal obligation to carry out testing when their property features hot/cold water systems and wet cooling systems under the Approved Code of Practice: Legionnaires' disease: Control of Legionella Bacteria in water systems (L8) from the HSE.

What is Legionnaires Disease?

Legionnaires’ disease is a form of atypical pneumonia, meaning that it causes inflammation in the lungs. This particularly affects the small air sacs known as alveoli which are important for drawing oxygen from the air. With Legionnaires’, legionella bacteria enter the lungs contained within small water droplets suspended in the air and then cause the aforementioned inflammation with symptoms typically appearing up to 10 days after first contact. The NHS lists fever, chills, a heavy persistent cough, difficulty breathing and flu-like symptoms as known symptoms of the disease.

What are the Risk Factors for Legionella?

Legionella bacteria are present in many different water systems but only begin to pose a threat when their growth is encouraged by environmental factors. Temperature is one of the most important factors when considering legionella risk as the bacteria grow fastest between 25˚C and 40˚C.

Another common issue is inadequate circulation of water. Water that is allowed to stand will become stagnant, thereby encouraging bacterial growth whereas good circulation moves the bacteria through the system before they become a problem. However, this can be negated by debris or corrosion in pipes and tanks which can provide shelter for the bacteria.

Finally, as legionella poses a risk as an airborne bacterium, any system which creates droplets of water, for example showers or cooling towers, needs more thorough inspections.

How do I Test for Legionella Bacteria?

Legionella testing should be carried out by a water service provider or an appropriately qualified individual. As far as the mains water supply is concerned, ground water in the UK has an average temperature of around 12˚C with surface temperatures varying between 4˚C and 23˚C. In an exceptionally hot summer, extra precautions may need to be taken, for example ensuring increased water flow through the system.

With cold water systems, an annual inspection of the cold water storage tank should be carried out in order to see whether the tank requires cleaning. Excess stagnation may also indicate that the tank is too large or not being used. Monthly temperature and disinfectant concentration testing should be carried out at points which best represent the system as a whole (sentinel points), usually the furthest tap and nearest tap to the storage tank or supply.

When it comes to hot water systems, temperature checks on primary circulating loops and non-circulating systems should be carried out monthly at sentinel points. For tertiary or subordinate loops, quarterly testing is recommended. We stock a number of different Legionnaires' temperature kits from the likes of Martindale, TPI, Testo and ETI which are intended for precisely the purpose of temperature monitoring in water systems.

Where cold water is above 25˚C or hot water below 50˚C, it is advised to have a sample tested by a UKAS-accredited laboratory that is a member of a microbiology proficiency testing scheme run by Public Health England.

How do I Prevent Legionella Growth?

Temperature control is one of the most important factors when it comes to preventing legionella growth. Cold water systems should run at a temperature lower than 25˚C whilst hot water systems should run at over 50˚C. It is also important to keep pipes and tanks clean and clear of debris and corrosion to prevent bacterial build up when water is flowing through. Finally, ensuring a continuous flow of water through the system will prevent stagnation. These simple steps go a long way to minimising the chances of anyone developing Legionnaires’ disease.