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Legionella Facts

Friday 14 March 2008

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Legionnaires' disease is a disease caused by the organism LEGIONELLA PNEUMOPHILA, which is found naturally in water and soil where it is normally harmless. But when it gets the right conditions of temperature, nutrient supply and pH, it multiplies rapidly, and if there is aerosol formation and a susceptible population, these are all the ingredients for an outbreak. The term "Legionnaires' disease" was first coined to describe an explosive common source outbreak of pneumonia caused by an unknown agent afflicting persons attending an American Legion Convention in Philadelphia in July 1976. Of 192 diagnosed cases, 20 were fatal. Examinations of lung tissue from some of the fatal cases demonstrated the presence of a previously unknown organism which was eventually called LEGIONELLA PNEUMOPHILA. Although there are at least 54 species of legionellae, Legionella Pneumophila is by far the most important human pathogen.

Legionnaires' Disease mainly affects adults, with men being more at risk than women. The greatest incidence of disease is in men over 40 years of age who also smoke. Persons who are immuno-compromised or suffering from respiratory disorders are also at higher risk. Infection is by inhalation of contaminated water droplets.

If antibiotic therapy of the appropriate kind is not applied soon after diagnosis, significant mortality can result.

Incidence in the natural environment

Legionella are natural aquatic bacteria occurring widely in the natural aquatic environment but most frequently in water at temperatures between 20°C and 50°C. They have been isolated from rivers, lakes, ponds, thermally polluted waters, mud and natural thermal ponds. They have even been detected on the canopy of tropical rain forests.

Incidence in the man-made environment

In a survey carried out by the PHLS in England and Wales between 1981 and 1985, 53% of hotels, 70% of hospitals and 75% of business premises studies contained legionellae in at least one sample from their hot and cold water systems.

Sources of outbreaks have been in hot and cold water systems, cooling towers, spa baths and oil/water emulsions used for lubricating lathes, misting devices, decorative fountains and water features, dentistry tools, TMV's (blending valves) etc.

The following are some examples of other causes of outbreak:

Sauna Linked to Fatal Legionnaires' deaths - Researchers in the Netherlands have traced six cases of Legionnaires' disease, two of them fatal, to a sauna. Health records dating back to 1991 revealed that the six cases were related to the same building. One of the fatalities was a woman who had had a kidney transplant and died 10 days after frequenting the sauna. The other fatality was a 59 year old man who had no history of immunosuppression. In another case, a 64 year old man was diagnosed with Legionnaires' disease after regularly using a footbath in the sauna. Testing revealed that his disease was caused by the same Legionella pneumophila strain as found in the woman who died. The man was treated and recovered from acute pneumonia caused by L.pneumophila. Dr.J.W.Den Boer of the Municipal Health Service in Haarlem, the Netherlands, and colleagues at other sites in Haarlem, report that water from the air-perfused footbath was tested and found to contain the same strain of L.pneumophila. In light of the cases, the sauna operators changed the hot water installation of the facility to prevent water from standing or flowing too slowly. The water is also tested regularly.

A cleaner at a small food outlet in Nottingham died from filling his bucket. Legionella was found within the pipework (29,000 sero group 1) the temperature of the hot water services was 40 ºC.

An automatic misting machine used to keep vegetables fresh in a Louisiana supermarket caused a major outbreak of Legionnaires disease, with 34 confirmed cases and two deaths. Noting that the victims tended to be shoppers at a certain supermarket, investigators found the responsible bacteria, Legionella pneumophila contaminating the store's misting machine. A similar instance occurred in a luxury hotel in the UK, two people died from inhaling the aerosols created by the salad bar whilst choosing their lunch.

Survival and growth in the environment

Legionellae are widespread in the aquatic environment and can survive in water for prolonged periods, but cannot grow by themselves. In nature they grow in association with other natural aquatic micro-organisms which presumably provide them with nutrients. Organisms supporting their growth include other aquatic bacteria and protozoa.

Aquatic micro organisms prefer to colonise surfaces rather than grow in the liquid phase because this provides them with a nutrient advantage and also renders them more resistant to adverse physical and chemical environmental conditions. The layer of growth formed on the surface is called a "biofilm". To control the growth of legionellae in man-made systems it is essential that the growth of other aquatic organisms and the development of biofilms are limited.


Prosecutions have been taken under the Health & Safety at Work Act 1974, and under the Control of Substances Hazardous to Health Regulations 1988. Therefore compliance is essential. In order to do this, the recommendations of the Approved Code of Practice (L8) will have to be fulfilled. Practical guidance on how to fulfil the conditions of the ACOP is contained in the same document, L8.