How to Test for Legionella

How to Test for Legionella

Legionnaires’ disease is an illness caused by Legionella bacteria, and it is most commonly contracted in work settings, healthcare facilities, and hotels.

Legionella bacteria are most commonly detected in water which is between 20-45°C, or stagnant. When people inhale tiny water droplets that contain particles of Legionella bacteria they can contract pneumonia. Legionella bacteria can cause a type of pneumonia that is deadly and it mostly puts the elderly, people with compromised immune systems, smokers, and alcoholics at particular risk. 

Atomisers, calorifiers, cooling towers, wet air conditioning plants, hydrotherapy baths, showers, domestic hot and cold water systems, dead legs or low-use areas are where Legionella are most likely to inhabit. 

All water hygiene regimes should prioritise the absence of Legionella. If water systems are managed properly, Legionnaires’ disease can be removed from them. It is imperative for us to be able to achieve this as the disease can be fatal in some cases. Employers and landlords are obligated by law to provide clean water for stakeholders, so it is in their interest to be able to make sure there is no Legionella in water they are responsible for providing. 

Pontiac fever is another illness that is caused by Legionella bacteria. The symptoms of Pontiac fever are mild symptoms that are similar to that of the flu. Fever, headaches, and muscle aches are some of the symptoms that are associated with Pontiac fever.

First Steps in Preventing Legionella Bacteria

A professional should be appointed to assess the risk of Legionella bacteria growth in the hot and cold water systems of a building. As every building is different, the professional responsible for the detection of legionella in a water system should be aware of how the water system in a building works. To consider the risks of Legionnaires’ disease on a site the professional must undertake a Legionella Risk Assessment, and have apt Legionella training.

How Frequently Should Legionella be Tested For

When a Legionella Risk Assessment is conducted a risk level is established, and from this, when, and how often you should test for Legionella can be deduced. In a situation where there is uncertainty around the results of the risk assessment, a weekly test for Legionella is a good rule of thumb for a water system. The frequency of Legionella testing should be reduced when a method to remove Legionella from water has proven effective.

The frequency of testing needed could be altered by environmental changes and the usage level of water systems. 

What Causes Legionella in Water to Grow?

There are certain environmental conditions that are conducive to the growth of Legionella bacteria. In warmer periods of the year air conditioning systems are used more often, which helps Legionella growth. Also, in situations where water systems get shut down (during low-demand periods), Legionella bacteria growth can also be stimulated in stagnant reservoirs. 

How to Test for Legionaella

There are several things to look out for when trying to detect risk levels from Legionella bacteria in a water system. 


Corroded pipes, valves, and fittings promote biofilm formation by protecting Legionella bacteria from being disinfected. To detect corrosion, rust-coloured (brownish, orangish) water, flakes or particles should be identified. 


The presence of scale also promotes Legionella growth. Usually be accompanied by whitish or off-whitish deposits on taps, showerheads, and internal plumbing. 


The presence of dirt, debris, or particulate matter can also promote Legionella bacteria growth. If water is cloudy or browny that is a good indication that there is sediment in the water that could contribute to this.

There’s a few different ways to test for Legionella bacteria, and the technology used to test Legionella has changed progressively over the years. There are pros and cons that apply to each method of testing, but by requesting the help of an expert you will be able to tell which method of testing is the most suitable for you. 

The Lab-based culture method

The most common way to sample water is the bottle bulk water sampling method. With this method, water can be collected from potable water or from mechanical equipment that has warm water in it. 

A UKAS accredited laboratory will be the next destination for the water sample. In the lab, professionals will attempt to detect the bacterial count and Legionella presence within each sample. There is a prime position in any water system that water should be sampled from, and an optimal way that samples should be collected to achieve the accurate outcomes. Samples should also be transported properly and in a timely manner. 

Unfortunately, the lab-based culture methodology can take some time to achieve a conclusion. 

The PCR (polymerase chain reaction) technique

This method is not as much of a time-consuming process as the culture method, and can be carried out in a matter of hours by following these steps: 

  1. By way of membrane filtration, viable cells should be concentrated. 
  2. These cells should then be made lyse and the DNA should be made free by way of sonication and heating procedures.
  3. The DNA should then be purified. 

Legionella can be identified quickly by using the PCR method. It is capable of detecting Legionella in scenarios where more traditional methods are unable to. Unfortunately, conducting the PCR method can be a more expensive way to test for Legionella, but in situations of outbreak, the PCR method is the most suitable. 

The rabid swab technique

There are now rabid-swab testing kits that are readily available. Such kits can detect Legionella in 25 mins. The fatal SERO group 1 strain of Legionella can be identified using such kits, and being able to detect Legionella so quickly can help in lessening the likelihood of human infection. While these tools are a useful self-test toolkit, it should not be considered a replacement for a thorough water testing programme that would be administered by a UKAS accredited lab. 

It is extremely important that we do what we can to prevent the growth of bacteria such as Legionella and its potentially fatal effects. By making sure water systems in your building have measures implemented that will deter or prevent the growth of Legionella bacteria, stakeholders can be protected. At Techmate we offer easy, safe and reliable Legionella testing kits that produce quick results. We also have a broad range of lab supplies on offer, if you need help picking one out get in touch with us