What is legionnaires disease?
Legionnaires disease is one of a group of pneumonia-like illnesses collectively known as legionellosis.
Where is legionella found?
Legionella bacteria are widespread in natural sources of water. They are also found in many recirculating and hot and cold water systems. Outbreaks of legionnaires' disease have occurred in or near large building complexes such as hotels, hospitals, offices and factories.
If legionella is so widespread, why aren't more people affected?
Infection is caused by people breathing in fine water droplets contaminated with legionella bacteria. For infection to occur a chain of events has to take place and fortunately this happens rarely. The chain includes:
- Conditions suited to the multiplication of the organism in water, i.e. water temperature in the range 20°C to 45°C.
- The presence of sludge, scale, rust, algae and organic matter to provide nutrient.
- Means of creating water droplets (such as a cooling tower or tap).
- Inhalation of the droplets by a susceptible person.
Cooling towers, which are wet or evaporative condensers that form part of an air conditioning system, can present a particular hazard because they readily generate fine water droplets and there is an air current to transport them. As they are usually located on rooftops there is a potential for infecting large numbers of people. The bacteria may also colonise hot and cold water systems - showers and spa baths have been associated with infection.
How can the risk be reduced?
Since legionella is widespread in the environment, it cannot be prevented from entering water systems. However, taking the following precautions can reduce the risk of an outbreak developing:
Hot and cold water systems - design and servicing
- Cisterns and pipe work should be designed so that water is not allowed to stand undisturbed for long periods;
- Cisterns should be well covered to prevent the entry of dirt, debris and vermin, and should be periodically inspected, cleaned and disinfected;
- Water temperatures between 20°C and 45°C should be avoided by insulation of cold water tanks and pipes in warm spaces, and by storing hot water at 60°C and circulating at 50°C. Where there is a risk of scalding for the very old, and young children, thermostatically controlled taps may be needed;
- Only water system fittings and materials which comply with water authority bylaws should be used (certain materials, e.g. leather, some rubbers and plastics, support the growth of bacteria and should not be used).
Cooling towers
- Cooling towers and their associated water systems need to be well designed, maintained and operated; the fitting of efficient drift eliminators which reduce the escape of spray is especially important;
- Systems should be cleaned and disinfected at least every six months;
- Water should be treated to prevent scale, corrosion and microbiological growth;
- Where reasonably practicable, cooling towers should be replaced with dry cooling systems.
Precautions are necessary wherever water conditions are likely to support the growth of bacteria and there is a means of dispersing droplets, e.g. commercial spa baths and humidifiers.
What are the legal duties?
The Health and Safety at Work Act and the Control of Substances Hazardous to Health Regulations both apply. Practical guidance on the legal duties is given in an approved code of practice from the Health and Safety Executive (HSE). A wealth of information can be found on the HSE's legionella pages at:
http://www.hse.gov.uk/legionnaires/
Owners of premises using wet cooling towers and/or evaporative condensers must notify the Borough Council that they have this equipment. Notification enables environmental health officers to carry out proactive inspections and provide vital information before an outbreak of Legionnaires' disease occurs.
For further information please contact the Environmental Health Team on 01256 844844, or by email at ehteam@basingstoke.gov.uk
