Legionellosis is an acute infectious disease that is caused by Legionella and is associated with two clinically and epidemiologically distinct illnesses: Legionnaires’ disease and Pontiac fever. Legionnaires' disease is characterised by pneumonia (Legionella pneumoniae pneumoniae). Pontiac fever produces a milder flu-like, non-pneumonic illness.

What are the symptoms of Legionnaires' disease?
The average incubation period for Legionnaires' disease is 2-10 days, in rare cases up to 20 days. Legionnaires' disease is characterised by pneumonia accompanied by fever, cough, dyspnoea, muscle aches and headache. On average, in 25-50% of patients diarrhoea and episodes of transient loss of consciousness may occur.

What causes Legionnaires' disease?
The genus Legionella contains more than 50 species, of which at least 20 have been associated with human infection. Legionella pneumophila is the major causative agent of Legionnaires' disease in Europe.

What is the most common way of contracting Legionnaires disease?Legionnaires' disease is most commonly contracted by inhaling aerosols containing Legionella bacteria or by inhaling contaminated water into the lungs. The disease does not usually spread from person to person. It is not contracted by drinking water.

Who is at higher risk of developing Legionnaires' disease?
Although Legionella bacteria is a natural inhabitant of water, the susceptibility of humans is very low.
Some people are at higher risk of developing Legionnaires' disease: older people, smokers, people with diabetes, chronic lung disease, oncological diseases and other diseases or conditions that suppress the immune system.

How is Legionnaires' disease treated?
Legionnaires' disease is treated with antibiotics. If you develop symptoms of pneumonia, contact your doctor as soon as possible. If you have stayed in private accommodation such as hotels, swimming pools or health care facilities in the two weeks before you developed symptoms, tell your doctor.

Where are Legionella bacteria found?
Legionella concentrations are usually low in natural waters, such as rivers and lakes, and moist soil6 but Legionella bacteria can easily proliferate in hot and cold water systems where conditions are right and appropriate controls are not in place.

What conditions are favourable for the amplification of Legionella?
Optimal growth is at temperatures between 20 and 45ºC. Sediment, scale, deposits, biofilm – support not only Legionella growth, but also the growth of the very important supporting microbiota for Legionella.

What are the potential sources of Legionnaires' infection?
Sources of aerosols that have been linked with transmission of Legionella include cold and hot water systems, shower heads, toilet cisterns, cooling towers, steam condensers, swimming pools, therapeutic baths, hot springs, fountains, automatic sprinkler systems, respiratory equipment, car wash services, humidifiers, irrigation systems, etc. Legionella bacteria can proliferate in pipes with poor or no circulation of water, in pipes covered with limescale or rust particles or other sediments, in showers and taps, in dirty, sludge-covered pipes, and on the inside surfaces of containers.

How can Legionnaires disease be prevented?

The key to preventing Legionnaires' disease is a proper operation of water systems. Proper maintenance of water temperature in water systems is one of the main ways to prevent Legionnaires' disease. Hot water at the outlet should not be less than 50ºC. At 60ºC, 90% of the L. pneumophila population are killed within 2 minutes. Cold water should be at least 20°C. It is important to maintain and clean showers, showerheads and taps to prevent sediment build-up, clean and disinfect water tanks, etc.
In cold water systems, the main means of killing Legionella bacteria is the use of oxidising biocides.


Last updated: 29-03-2024