Legionella outbreaks can occur if you do not test water systems regularly or thoroughly.
Testing is essential for protecting people’s health and mitigating the risk.
Where Does Legionella Occur?
The legionella pneumophila bacterium occurs naturally in the world around us.
Water sources such as lakes, streams and rivers can contain low levels of legionella.
Typically, these are not dangerous when people are exposed to them.
However, legionella can also build up in man-made water systems and these can create conditions that permit the bacteria to grow to levels that are dangerous.
These man-made water systems include:
• Shower heads and sink taps in domestic water systems
• Fountains and water features
• Water tanks
• Water coolers and towers
• Large plumbing systems
• Hot tubs, thermal spas and pools.
Legionella can thrive in warm temperatures, and where it comes into contact with other environmental organisms.
How Often Should You Carry Out Legionella Testing?
How often you should test for legionella depends on the circumstances and conditions of your location.
These factors help determine the level of risk from legionella contamination.
Therefore, before considering how often to test for legionella, you should carry out a legionella risk assessment.
This involves a full assessment of your water systems and anything else that uses water, such as processing equipment, cooling towers, and spa pools.
When conducting this risk assessment, you must examine pipework, water tanks, boilers, taps, showers and other outlets. Essentially, anything that uses water.
HSE has an approved code of practice and guidance, known as ACOP L8 Regulations, which recommends regular legionella risk assessments.
It is especially important to keep records up to date, and to reassess systems for risk after there have been any changes.
A legionella risk assessment will indicate how often you should test for legionella.
HSE recommends quarterly testing as a minimum for open systems, such as cooling towers and spa pools. Closed systems generally pose much less of a risk because they are not exposed to the elements.
However, where there is any doubt about how effective your legionella control regime is, you should test these systems.
As for legionella risk assessments, you should carry these out every two years at least.
How Do You Test for Legionella?
Under HSE guidelines, you should appoint a competent person to carry out legionella testing. This needs to be someone who is properly trained and supervised to undertake this task.
Generally, this will be a service provider, such as a professional water treatment professional.
The testing process must be compliant with BS 7592, which governs the sampling of legionella bacteria in water systems.
This gives recommendations for processes and materials for sampling water to test it for legionella. It provides key standards and recommendations for routine monitoring, as well as investigating legionella outbreaks.
The legionella testing process involves an appointed person visiting the site and taking samples.
The sample is collected in a sterile water sample bottle or with a swab. The sample-taker must be careful to avoid any contact with taps, pipes or other potential contaminants.
HSE states that water samples must be tested by a UKAS-accredited laboratory.
Using a legionella testing kit, the lab will then test the sample for legionella. There are various methods for doing this.
The polymerase chain reaction (PCR) method, is a rapid testing technique, involving the amplification of small segments of DNA from the sample.
Alternatively, the culture method will detect legionella colonies on BCYE agar, a buffered charcoal yeast extract. However, this is a much slower testing method.
A third method involves the use of fluorescence microscopy to detect the presence of specific antigens in the sample. This is known as a direct fluorescent antibody (DFA) test.
How Much Do Legionella Tests Cost?
The cost of a legionella test will vary according to the number of water services involved and the size of the site requiring testing.
Typical costs can start at around £200, but will rise according to the complexity of the site. For example, hotels and hospitals can have larger systems with several tanks, cylinders and other water system components.
What Happens After Testing?
A major aspect of water management is controlling legionella to minimise its growth. You can achieve this using a disinfecting water treatment to remove biofilm, a major source of bacteria.
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