30th June, 2022

The 12 Symptoms Of Legionnaires Disease That Can Be Fatal

Legionnaires' disease is an infection caused by breathing in small droplets of water contaminated by the Legionella bacteria. It is a severe form of pneumonia that can be fatal. Learn more about Legionnaires' disease and the 12 symptoms to look out for.

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While relatively rare, there are around 350 confirmed cases of Legionnaires' disease identified in the UK each year. The fatality rate is around 10% for healthy people and up to 40% for vulnerable people.

What is Legionnaires' disease?

Legionnaires' disease is a severe form of pneumonia that can be fatal.

It is caused by inhaling water that is contaminated with Legionella bacteria. It is this bacteria that causes the infection within your respiratory system, making you ill.

Legionnaires' disease is a serious and potentially fatal lung infection, so it is important to be able to spot the symptoms early and take action.

Unfortunately, because the symptoms are very similar to flu, treatment may be delayed. The elderly and the young are especially at risk due to having weaker immune systems to fight the illness.

Legionnaires' disease is a serious illness and deaths may occur in approximately 10-15% of otherwise healthy individuals. The number of deaths reported may be higher (up to 40%) in some groups of patients, such as those who have weakened immune systems.

How do you catch Legionnaires' disease?

You can catch Legionnaires' disease if you breathe in tiny droplets of water from a contaminated water source that contains the Legionella bacteria.

You won't usually get Legionnaires' disease from drinking contaminated water, but instead when the droplets are inhaled and the bacteria enters your lungs.

Legionella bacteria are found in natural water sources, but usually in low numbers so that it doesn't pose a risk to human health. But if the bacteria contaminate and grow in water systems, it can become a problem.

Where could you get Legionnaires' disease?

Any water system could potentially be a source for legionella bacteria growth. Particularly where water is stored at the temperatures where legionella bacteria can thrive.

Many of the water systems in larger buildings like offices, hotels and hospitals will have the potential to grow and spread the bacteria if not controlled.

Remember, you catch Legionnaires' disease by inhaling the legionella bacteria. Any system that creates a fine spray of water can spread the disease to humans.

You are most likely to get Legionnaires' disease from:

High-risk systems can include air conditioning systems, water towers and other water storage.

water storage tank

What are the symptoms of Legionnaires' disease?

Legionnaires' disease symptoms include:

  1. A bad cough that doesn't go away
  2. Trouble breathing
  3. Muscle aches and pains
  4. Tiredness
  5. Severe chest pain
  6. A headache
  7. High temperature
  8. Feeling hot and shivery
  9. Feeling like you have severe flu
  10. Pneumonia (when illness develops)
  11. Diarrhoea (occasionally)
  12. Signs of mental confusion (occasionally)

These symptoms aren't likely to start straight after you are exposed to a contaminated water source, as the disease can take days, and even weeks to develop, and gets progressively worse over a few days.

What should you do if you think you have Legionnaires' disease?

Due to the similarity to flu symptoms, it is not easy to diagnose Legionnaires disease. If you suspect Legionnaires disease you should contact your doctor, and let them know if you have been at any high-risk places in the last 10 days, like a spa or hotel.

The diagnosis may be made with a blood or urine test, and you might need to go to the hospital for further tests and treatment.

Once the symptoms have been spotted and Legionnaires' disease has been diagnosed, it's important to establish where it was caught, as others will be at risk.

If you suspect you have developed the illness through work you must report it to your employer.

What are employer duties?

There is a legal requirement for employers to report cases of Legionnaires' disease that may be acquired at their premises to the HSE.

Employers are required to carry out risk assessments for activities that may create risks to their workforce, and to reduce the risks as far as is reasonably practicable.

washing hands

Duties under the Health and Safety at Work etc Act 1974 extend to risks from Legionella bacteria, which may arise from work activities. The Control of Substances Hazardous to Health (COSHH) Regulations also cover bacteria.

Employers should:

You can raise awareness with the Legionella Toolbox Talk.

How can employers reduce the risk of Legionnaires' disease?

A well maintained and managed water system should prevent the growth of legionella bacteria. This will often involve a combination of temperature control, monitoring, and treatment.

If you're not comfortable managing the risks of Legionnaires' disease yourself, you should appoint a competent person to assist you.

There may be a risk of exposure to legionella bacteria in any workplace, due to the presence of water systems.


There is an increased risk where water is stored within a water system, as this gives the bacteria time to grow. The legionella risk within water systems must, therefore, be managed and controlled.

A risk assessment of the water system can be carried out to identify and assess sources of risk, and to put in place the necessary precautions to address any hazards and prevent or control the risks present.

Download our Legionella risk assessment template for help conducting a comprehensive risk assessment of your water system.

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This article was written by Emma at HASpod. Emma has over 10 years experience in health and safety and BSc (Hons) Construction Management. She is NEBOSH qualified and Tech IOSH.

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