Legionnaires' disease (legionellosis) is a severe, often fatal pneumonia. It mainly affects adults. Legionnaires' disease is caused by bacteria (legionella).

Hot water supply systems of large buildings (hospitals, nursing homes, old people's homes, accommodation facilities, spas, less frequently of residential complexes), artificial water-bearing systems (cooling towers, whirlpools, humidification systems, indoor decorative fountains, pool baths, thermal springs and their distribution systems)

Legionella are widespread environmental germs that occur in small numbers in surface waters and groundwater, but also in moist soils, mixing soil for potted plants, humus and compost.

By inhalation of very fine water droplets (aerosols) or fine dusts contaminated with Legionella.

Severe pneumonia

Despite the availability of effective antibiotic treatment and the lack of evidence of antibiotic-resistant pathogens, between 10-15% of people affected by Legionnaires' disease die each year.

The most important measure is the elimination of possible sources of infection

In Austria, every suspected case, case of illness and case of death must be reported. The risk of contracting Legionnaires' disease by inhaling fine dust particles containing legionella from plant soil or compost is very low (two documented cases in 2009).

Legionella are rod-shaped, sporeless, gram-negative bacteria grouped in the family Legionellaceae. The single genus Legionella subsumes over 40 named species with more than 60 different serogroups, only a small number of which are pathogenic to humans. The epidemiologically most important species is Legionella pneumophila with at least 15 serogroups, whereby serogroup 1 has been detected in about 90% of human legionelloses in Austria.

Legionellosis (Legionnaires' disease) is a severe, often fatal pneumonia, mainly caused by inhalation of aerosol contaminated with Legionella pneumophila or, more rarely, with other Legionella species. The bacterium can occur in hot water supply systems of large buildings such as hospitals, nursing homes, retirement homes, lodging houses, spas, less commonly residential facilities, and in other man-made water-bearing systems where it finds conditions conducive to reproduction (such as in water-bearing systems of cooling towers, whirlpools, humidifiers, indoor decorative fountains, pool baths, or in natural thermal springs and their distribution systems) in numbers of concern to humans. Legionnaires' disease primarily affects adults. Despite the availability of effective antibiotic treatment and the lack of evidence of antibiotic-resistant pathogens to date, between 10-15% of people affected by Legionnaires' disease die each year. The most important measure in the fight against this infectious disease is therefore prevention.

Transmission

Inhalation of legionella-contaminated aerosols (finest water droplets) or fine dusts can lead to severe pneumonia, the so-called Legionnaires' disease. Drinking water contaminated with legionella does not pose a health risk. People with weakened immune systems, chronic lung disease, and smokers are at increased risk. Transmission from person to person is not possible.

In Europe, Legionnaires' disease is mainly caused by Legionella pneumophila. However, there are also other Legionella species that are widespread in the environment and can also lead to infection under certain circumstances. Increasingly, cases of Legionnaires' disease caused by the species Legionella longbeachae are being recorded worldwide, particularly in Australia, but also in Europe. The source of infection in these cases is probably commercially available plant soil, as was the case in a fatality in Austria in 2008. The risk of contracting Legionnaires' disease by inhaling fine dust particles containing Legionella from plant soil or compost is very low: in 2009, two cases were documented by us. In Australia, where Legionella longbeachae infections are more widespread, plant soil is labelled with a risk notice and it is recommended that soil be moistened before use to avoid dusting, gardening gloves be worn and hands be washed thoroughly after work. Wearing fine dust respirators is also sometimes advised for handling plant soil.

Prevention

After the discovery of the infectious disease in 1976, national surveillance systems for Legionella infection were established in many countries. In Austria, every suspected case, case of illness and case of death must be reported. Epidemiological surveillance based on reports from physicians and laboratories together with the surveillance system of the National Reference Centre for Legionella Infection enables rapid identification of clusters. The competent district administrative authorities, with the support of our infection epidemiologists, can carry out an adequate outbreak clarification with prompt identification and elimination of the source of infection.