Last updated: 21.06.23

Legionnaires’ Disease UK: Identification, Treatment, and Prevention

Legionnaires’ Disease UK: Identification, Treatment, and Prevention

Every year, waterborne diseases impact hundreds of millions of people across the planet. Whilst this is primarily the case in underdeveloped countries in which residents do not have access to sanitary and safe water supplies, developed countries, such as the UK, are also still affected by waterborne infections and diseases. 

Legionella is just one example of a waterborne pathogen that continues to impact residents of the UK year after year. The bacteria itself can cause several conditions, the most severe of which is Legionnaires’ Disease. If not treated appropriately, it can be fatal. 

Given it is a waterborne disease, Legionella can theoretically be encountered by anyone in the UK who has access to natural water sources and who uses purpose-built water systems. This means that individuals need to be aware of how they can mitigate the risks of contracting Legionella, and therefore Legionnaires’ Disease, as well as knowing the symptoms of this illness and what to do if infected.

That’s exactly why we’ve gone into detail about what Legionnaires’ Disease is, alongside how to identify, treat, and prevent the illness, to ensure the safety of yourself, and others, whether at home or in working environments.

What is Legionella and What is Legionnaires’ Disease?

Legionella is a form of bacteria, known as Legionella pneumophila. The bacteria has been known to cause a less-severe illness known as Pontiac Fever, but it is more commonly known for being the cause of a significant condition known as Legionnaires’ Disease. 

Legionnaires’ Disease is a severe form of pneumonia caused by breathing in small water droplets in the air that contains the Legionella bacteria, which may have come from devices such as air conditioners or hot tubs. The name of the disease comes from the first recorded outbreak, which occurred at the 1976 American Legion convention in Philadelphia. 

Due to the nature of Legionella, it accounts for less than 10% of the total number of pneumonia cases, and outbreaks of the bacteria are even rarer. Sometimes, an individual who has been infected requires hospitalisation, however, there is only a small but significant mortality rate which is almost exclusively in at-risk groups. 

Where Can You Find Legionella Bacteria? 

The Legionella bacteria live primarily in freshwater, such as lakes, rivers, and reservoirs. But it can also be found in soils and other environments.

You can also find Legionella within purpose-built water systems such as hot and cold water systems, spa pools and hot tubs, evaporative condensers, and cooling towers. It is less common to find the bacteria within water systems at home. However, it is more likely that you will find Legionella in larger places such as hospitals, hotels, or offices, as the bacteria are more likely to have found their way into the water supply in these locations. 

What Causes Legionnaires’ Disease and How is Legionnaires’ Disease Spread?

Legionnaires’ Disease is usually contracted when a person breathes in water droplets that are contaminated with Legionella bacteria. In turn, the bacteria in this water infects the lungs, which causes pneumonia.

Due to the large and complex water system in many buildings, the bacteria can spread quickly. The bacteria grows and multiplies within these water systems, which increases its concentration and makes it more likely that individuals will breathe in contaminated water droplets. 

It’s important to note that Legionnaires’ Disease is not able to be spread from person to person. However, it has been said that this could be possible in very rare situations or circumstances. 

Similarly, Legionnaires’ Disease can’t usually be contracted by drinking infected water. However, this could be possible if an individual were to drink Legionella-infected water and accidentally breathe in some of these droplets whilst drinking. 

Legionnaires’ Disease Symptoms

The symptoms of Legionnaires’ Disease can be serious, persistent, and even debilitating. The symptoms displayed may vary from person to person, alongside their severity.

Symptoms of Legionnaires’ Disease include the following, which are also frequent symptoms of other forms of pneumonia:

  • Headaches
  • Flu-like symptoms, such as a fever
  • General body and muscle pain
  • Fever and/or chills
  • Confusion and tiredness
  • Chest pains
  • Difficulty breathing
  • A persistent cough
  • Gastrointestinal symptoms, such as vomiting, diarrhoea, and nausea

In rare cases, whilst Legionnaires’ Disease largely only affects the lungs of the infected individual, it has been known to cause infections within wounds and other organs of the body like the heart. 

If you suspect yourself, or another person, to have Legionnaires’ Disease in line with the above symptoms, then you should seek a GP appointment as soon as you can. However, if you or the person experiences severe coughing, chest pain, and difficulty breathing, then more urgent medical attention should be sought. 

Be aware that Legionnaires’ Disease has an incubation period in which no symptoms will be displayed, which is usually around a week. However, symptoms can arise anywhere between 2 and 14 days after being exposed to the Legionella bacteria. 

A medical professional will conduct a urine test to determine if a person has Legionnaires’ Disease. If this test comes back positive, you’ll be given medical advice and treatment accordingly. 

Who is Most at Risk of Contracting Legionella Disease? 

As with all forms of pneumonia, certain groups are significantly more at risk from Legionnaires’ Disease than others. These groups are as follows:

  • Older people: Older individuals are generally more at risk of contracting the disease, with the vast majority of cases in older individuals being over the age of 50 years.
  • Smokers: Smoking can make a person’s lungs more susceptible to infections. So those who are current smokers, or who have smoked in the past, are more susceptible to the disease.
  • Pre-existing medical conditions: Existing illnesses or conditions, such as lung disease, can make infection more likely and also lead to complications if the Legionella bacteria is contracted.
  • Those with weak immune systems: Individuals with a compromised immune system, such as people diagnosed with HIV or those who are taking medications that weaken their immune systems, can be more susceptible to Legionnaires’ Disease.

At-risk groups, whilst more likely to contract the illness in the first place, are also more likely to develop a more serious form of Legionnaires’ Disease. As a result, if they become infected, they may need increased medical attention to ensure their recovery. 

Treatment for Legionnaires’ Disease

The symptoms of Legionnaires’ Disease require medical intervention for the disease to disappear. Some patients are treated for Legionnaires’ Disease in hospitals but, in most cases, patients can stay at home for the duration of their treatment. 

Legionnaires’ Disease is typically treated with a course of antibiotics, which can either be administered orally or given directly into the infected individual’s vein. Other forms of treatment may include receiving oxygen to assist with breathing via tubes into the nose or a face mask, or even a machine to assist with respiration. 

Antibiotic treatment courses typically last between 1 and 3 weeks. If patients are in a hospital and begin to feel much better during their course of treatment, they can return home to finish their treatment. 

In the vast majority of cases, people will make a full recovery fairly quickly from the disease. Hospital admittance is rare amongst those who have Legionnaires’ Disease, and further complications are only likely amongst those with pre-existing medical conditions. 

In most instances, it takes multiple weeks for patients to feel back to normal after making a full recovery from the disease.

How to Prevent Legionnaires’ Disease

Legionnaires’ disease prevention is fairly straightforward, and most modern buildings will carry no risk of having their water supplies contaminated with Legionella. 

The most favourable conditions for Legionella growth include stagnant water. Thus, one of the ways to reduce the risk of harbouring the bacteria is by ensuring any dead ends in pipe works are removed and that infrequently used water outlets, such as taps or shower heads, are flushed out at least weekly. Similarly, it is important to descale shower heads, hoses, and other outlets at least every 3 months to prevent any build-up of Legionella on these devices, as the bacteria feed off of impurities such as algae and limescale.

The bacteria also thrive in warmer water between 20°C and 45°C, so provided that water supplies are kept below or above this range at all times, Legionella growth can be prevented.

What is Legionella Risk Assessment? 

A Legionella risk assessment is a technical review and evaluation to identify and assess any potential risks and hazards associated with pathogenic organisms, such as Legionella pneumophila. 

Conducting a Legionella risk assessment is a legal requirement in line with the Health and Safety at Work Act 1974 for building owners, managers, and landlords

The aforementioned individuals can conduct a risk assessment themselves if they have the skills and knowledge of health and safety to execute the assessment properly. Alternatively, employers or premise owners can appoint an individual to be responsible for managing and undertaking health and safety duties, which would include the practices involved with a Legionella risk assessment. 

If an external source is brought in to carry out a Legionella risk assessment, it is the responsibility of the competent individual within the company to ensure that the required standards for the assessment are met. 

The Legionella risk assessment will help in identifying the following, which could be a risk for Legionella:

  • If water droplets are produced and if they can be dispersed over a wide space
  • If water is re-circulated or stored within a system
  • If there are nutrients which Legionella could potentially feed off of, such as limescale or rust
  • Whether the water temperature in all parts of the system lies between 20°C and 45°C 
  • Whether there are optimum conditions in which bacteria could multiply
  • Whether particular employees, visitors, or residents are at an increased risk of Legionella infection, and if they could likely be exposed to water droplets with Legionella

Regardless of whether hot or cold water is within a system on a site, a risk assessment is still required to be carried out as there may still be elements of a system that could increase the risk of Legionella multiplying, such as dead ends in pipes or showerheads. 

How Often Should Legionella Testing Be Done?

Systems which are open, such as evaporative condensers, spa pools or hot tubs, and cooling towers, require Legionella testing at least every 3 months.

For those conducting Legionella risk assessments, these risk assessments should be reviewed at least every two years to observe that these evaluations are still up to date and, therefore, the safety of all individuals who could be exposed to systems that could contain Legionella is prioritised.


How Common is Legionnaires’ Disease?

Legionnaires’ Disease remains a largely uncommon infection. For reference, it is estimated that there are 4,000-6,000 cases of Legionnaires’ Disease annually in the UK. 

What are the Long-Term Effects of Legionnaires’ Disease?

If a person contracts the Legionella bacteria and develops Legionnaires’ Disease, this can be life-threatening. However, the majority of patients do make a recovery from the illness. 

Long-term side effects can occur amongst those who have had the disease, which typically include lack of energy and fatigue. These long-term symptoms can last for several months post-recovery. 

At What Time of Year is an Outbreak of Legionnaires’ Disease Most Likely?

Research has revealed that Legionnaires’ Disease is more likely to occur in warm and humid months of the year, meaning that summertime brings higher risks of people contracting Legionnaires’ disease. 


Legionella Disease can be a very serious illness which, if contracted, can pose great risks to the health of an individual. We hope that this article has provided you with the insight you need to understand Legionella and Legionnaires’ Disease in more depth as well as the ability to identify symptoms and mitigate the risks of yourself, or others, contracting the illness. 

If you are in any doubt as to how you can prevent Legionella from contaminating your organisation’s water supply, then our CPD-approved ‘Legionnaires’ Awareness’ course can offer you the training you require to understand how outbreaks of the disease can occur, and how you can mitigate the risks associated with this.