What you need to know about Legionella: symptoms, treatment and recovery

By: Alex Winter on Jul 11, 2019

Legionnaires' disease is an extreme form of pneumonia caused by Legionella bacteria. It can be caught by inhaling water droplets containing the bacteria. Legionella bacteria grow when water temperatures are between 20-45°C, where nutrients, such as rust, sludge, scale, sediment and algae are available, and also where water is stagnant in the water system (eg, if a shower or tap is not regularly used).

Contaminated water droplets can be created by many and varied methods including hot tubs, cooling towers, showers, taps, and industrial processes, wherever water is warm and a spray is produced.

It is rare to find it in the home where water turnover is generally good. It is most likely to be found in hotels, hospitals and factories – anywhere with industrial water systems. Although the bacteria can be present in ponds, lakes and rivers, these are not likely sources of infection.

In the UK almost half the known cases are associated with a trip abroad.

Is it contagious?

Because you have to inhale water droplets in order to catch the disease, it is generally not contagious, and it is usually safe to be around people with the disease.

What are the risk factors?

There are a few risk factors that make you more susceptible to the disease, the most prevalent being smoking, or chronic lung disease. People with organ transplants are also at higher risk and anyone who is taking corticosteroid medicines. Men are around three times more likely to contract the disease than women.

Who is vulnerable to the disease?

Although it is rare, Legionnaire’s Disease can be fatal, and the following groups are particularly vulnerable:

  • those who are 50 years or older
  • those with an underlying medical condition or pre-existing lung condition
  • those with a weakened immune system, e.g. people with cancer or HIV
  • those who smoke or drink alcohol heavily

It is extremely rare for babies or children to catch the disease.

What are the symptoms?

Legionnaire’s disease is a form of pneumonia, an infection that causes inflammation of the small air sacs in the lungs (alveoli) and their associated tissues. The initial symptoms of the disease usually show themselves around two to 10 days after infection. Unfortunately, there are no typical or unique symptoms associated with the disease and not everyone exposed to the bacteria goes on to develop symptoms. In general, early symptoms are similar to flu and may include:

  • high temperature, feverishness and chills
  • a dry cough
  • muscle aches and pains
  • loss of strength (asthenia)
  • headaches

If untreated the infection may become more severe within the first week, and infected persons may experience further symptoms such as coughing up green phlegm and becoming short of breath. They may have chest pain when breathing.

Some people who have Legionnaires’ disease suffer from nausea, vomiting, diarrhoea and abdominal (tummy) pain. Almost half of patients suffer from disorders related to the nervous system, such as confusion, delirium, depression, disorientation and hallucinations.

If you have these symptoms it is important to see a doctor as soon as possible – they may not be caused by Legionnaire’s but a doctor will be able to take steps to determine that.

In the UK you are advised to phone 111 or go to 111.nhs.uk if you have a bad cough and:

  • it does not go away
  • you cannot breathe properly
  • you have severe chest pain
  • you have a high temperature or feel hot and shivery
  • you feel like you have severe flu

As these could be symptoms of Legionnaires' disease.

Long term effects

In severe cases, Legionnaire’s can be fatal. Other serious complications can include respiratory failure, shock and acute renal and multi‑organ failure.

Although most patients will recover without ill effects after treatment, some may suffer from long term issues such as persistent pulmonary scars and restrictive pulmonary disease in patients who experience severe respiratory failure. In serious cases, there are often general secondary symptoms, such as weakness, poor memory and fatigue, which may last for several months.

Other neurological issues that can follow from severe infection include residual cerebellar dysfunction, retrograde amnesia, and other disorders of the nervous system.


Examination by a GP is the first step and it’s important for the patient to tell the doctor if they have been overseas, in a hot tub or spa, or if others in their social circle or workplace have shown similar symptoms, as these will be additional and important factors in determining a diagnosis of Legionnaire’s disease.

A urine test is generally used to look for the presence of legionella antigens (substances that cause the immune system to respond to the infection). A blood test may also be carried out to measure the antibodies in a patient’s blood.

It may be necessary for the patient to go to a hospital for an x-ray which can determine whether there is an infection in the lungs.


Like other forms of pneumonia, treatment generally consists of a course of antibiotics which are usually given straight away, without necessarily waiting for test results. However, this may not be effective, and if this is the case, then alternative antibiotics may be prescribed. In severe cases, patients may be admitted to a hospital where antibiotics may be administered through a drip.


Most patients should respond to treatment within three to five days. The majority of people with mild or moderately severe Legionnaires’ disease make a full recovery, although the length of that recovery may vary depending on how severe the condition is, whether the patient has any risk factors, how fit a patient is, how quickly treatment was commenced and whether any complications develop. Recovery can take as long as six months.

Legionnaire’s and the workplace

It is important to note that under UK Health and Safety regulations any outbreak or suspected case of Legionnaire’s must be reported:

  • If you suspect that your illness is as a consequence of your work then you should report this to your manager, as well as your health and safety representative and occupational health department, if you have one.
  • There is a legal requirement for employers to report cases of Legionnaires' disease that may be acquired at their premises to the Health and Safety Executive.

Because of the nature of the symptoms and the potential length of the recovery period, employees with Legionnaire’s may be off work for some considerable time.


Legionnaires is a form of pneumonia and presents severe flu-like symptoms. Early diagnosis is essential to reduce the impact of the disease and to prevent any serious consequences.

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Topics: Water Hygiene, Legionella

Alex Winter

Written by Alex Winter

Alex is a Marketing Contributor and has 5+ years in water treatment and ACoP L8 compliance and works across all six linked areas of the business; Water Treatment, Waste Water, Water Hygiene, Air Hygiene, Engineering and Legionella Training.