What are the symptoms of a Legionella infection?

Most people do not become ill after exposure to Legionella bacteria. If a person does become ill, the first symptoms usually start 2 to 10 days after exposure.

Legionellosis starts with flu-like symptoms, such as:

• headache
• muscle pain
• nausea
• diarrhoea
• fever
• dry cough

Very occasionally, a person with legionellosis may develop severe pneumonia. This is known as Legionnaires’ disease. This form of pneumonia can be so severe that people can die from it. Legionnaires’ disease almost never occurs in people under 40. 

A person with pneumonia will have symptoms like:

• shortness of breath, tightness or pain while breathing
• high fever
• cold chills
• possibly confusion

They will usually have to go to hospital and be treated with antibiotics. It could take a long time to recover completely. Somewhere between 2% and 10% of patients in the Netherlands who have pneumonia caused by the Legionella bacteria will die as a result. The risk of death is higher for elderly people.

Who can become very ill from legionellosis?

Some people have a higher risk of severe pneumonia caused by the Legionella bacteria:  

• older people (over 65)
• ​​​​​​​people who are less resistant to infection, for example because of a chronic illness
• ​​​​​​​people who are using immunosuppressant medication
• people who smoke

How might I catch legionellosis?

Legionella bacteria can be found in water and garden soil. If very small water droplets (mist) or particles of garden soil containing Legionella become airborne, a person can inhale the bacteria. If the bacteria enter the lungs, this can cause symptoms.

For example, a person might inhale Legionella bacteria in the following situations:

• while spraying water, such as from a shower, a garden hose with a spray nozzle, or a pressure washer
• in hot tubs that use air jets
• when using a certain type of wastewater treatment plant in which air is added to the water; when using devices that produce water mist, such as CPAP machines for treating sleep apnoea or air humidifiers
• when using wet cooling towers: water installations that cool buildings or industrial processes by producing water mist

People cannot get legionellosis by drinking water contaminated with the Legionella bacteria. An exception to this is people who have severe swallowing problems. They could become ill from contaminated water. A person who has legionellosis cannot infect others.

How can I prevent legionellosis?

You are very unlikely to become ill from Legionella bacteria in your own home. However, you can limit the growth of these bacteria by following these tips:

• Make sure that hot water from the boiler or combi boiler reaches a high temperature (at least 60 degrees).
• Are you in your mid-60s or older, and/or do you have any chronic health conditions? Then it is a good idea to replace the shower hose and shower head every 2 or 3 years, and arrange for any thermostatic taps to be cleaned.
• Do not make changes to the drinking water system yourself. Instead, have an official installation company handle the work. For example, it is important during installation to ensure that cold water cannot be heated by adjacent hot pipes (hotspots).

Regularly clean devices that mist or spray water. Do not leave water in these devices and dry them immediately after use if possible. For example: 

• Drain the garden hose, pressure washer and other spraying equipment or toys completely after use. Also empty the plant sprayer after each use. 
• Clean and disinfect a hot tub (e.g. a spa, whirlpool, jacuzzi, hot tub) regularly according to the instructions. Drain the bath after use. Is the hot tub in the garden? Then make sure no soil gets into the water. 
• Descale your shower head regularly. 
• Apnoea device (CPAP): fill the water reservoir with cooled boiled water and change the water every day. Clean the mask every day. Clean and disinfect the reservoir every week according to the instructions. 
• Humidifiers: fill with cooled boiled water. Clean and descale the reservoir regularly and change the water at least once a week. 
• Water birth: clean the bath before use and do not fill the bath until labour starts. Do not use baths with water circulation or heating. If you rent a bathtub, always use a hygienic cover.

You cannot get legionella-induced pneumonia from devices that maintain a constant temperature above 60°C or do not produce water mist. This includes coffee makers, electric kettles, containers of water placed on top of heaters, and steamers. 

You can lower your risk of pneumonia caused by legionella if you quit smoking.

Hospitals, nursing homes, saunas, swimming pools and overnight accommodations (including hotels) are required to take steps to prevent contamination with legionella.

Does flushing my water pipes after a holiday help prevent legionella?

Running the taps in your home after a holiday is a good way to refresh your drinking water supply. However, this is not the same thing as legionella prevention. If legionella is in the pipes, it will not be removed simply by flushing the pipes – not even if you run them for a long time. This is not usually a problem, since the Legionella bacteria that can make you ill are not usually found in household pipes. And even if they are present, people almost never develop severe pneumonia from exposure. However, it is a bigger concern for people in risk groups.

Is there any treatment for legionellosis?

Pneumonia caused by Legionella bacteria (Legionnaires’ disease) is treated with antibiotics. Most people recover from pneumonia after this treatment.

Tracking down the source

Every time a legionellosis patient is reported, the Municipal Public Health Services (GGDs) check how the patient might have been exposed. By identifying the source, the GGD aims to prevent more people from becoming ill. Despite these efforts, the source of the exposure remains unknown for many patients.

How common is legionellosis?

In recent years, there have been about 400-680 reported cases of legionellosis in the Netherlands per year. About 100 to 150 cases reported annually involved people falling ill after travelling abroad. The actual number is higher, since not all patients can be properly examined. There are usually more patients with legionellosis in summer than in winter. Damp weather also seems to have an impact.