Legionnaires Disease

What causes Legionnaires Disease?

This disease is caused by Legionella bacteria.  There are over twenty species of Legionella, of which Legionella pneumophilia is responsible for many of the cases.

Legionella is a bacteria associated with water and is widespread in the environment.  It has been found in lakes, rivers, creeks, hot springs and other bodies of water and soils.  Legionella is also found in artificial environments such as cooling towers associated with air conditioning and industrial processes, as well as in reticulated warm water systems, where the temperature of the water is kept between 30C and 50C.  These artificial systems can provide conditions, which allow the bacteria to breed to large numbers.

How do you get Legionnaires Disease?

Infection is known to be acquired through breathing in aerosols (very fine droplets of water) which contain the bacteria.  It is not passed from person to person nor is it acquired through drinking Legionella contaminated water.

Where are cooling towers found?

Cooling towers are used to provide cooling for a variety of industrial processes, including refrigeration and freezer plant, commercial size air conditioning and water-cooled compressors.  A prime function of cooling towers is to recirculate water that would otherwise be run to waste.  Evaporative condensers, which incorporate a refrigeration condensing coil, are regarded as cooling towers in relation to health aspects.

Why are cooling towers a problem?

During the normal operation of a cooling tower, aerosols are formed which will be carried into the environment through the tower exhaust.  If Legionella are present in the tower water, breathing the aerosols can result in infection.  Poorly maintained cooling towers have been implicated in outbreaks of Legionnaires' Disease overseas and Australia.

What about other sources of Legionella Bacteria?

• Warm (tepid) water systems in health care buildings, institutions and commercial buildings
  These are also required to be registered, except for those in domestic premises.  Systems using thermostatic mixing valves generally do not need to be registered.  Contact the Public and Environmental Health Service for more details.
  
• Spa pools
  These are regulated under Place of Public Assembly provisions of the Public Health Act 1997
  
• Potting mixes used in horticulture by home gardeners
  These are not regulated by the Public Health Act, but carry recommendations about safe handling.

Where can I get more information?

Copies of AS/NZS 3666.2 are available from Standards Australia, 237 Elizabeth Street, North Hobart, 7000, Ph (03) 6231 5885, Fax (03) 6231 5886, website www.standards.com.au.

This information was compiled by the Public and Environmental Health Branch, Department of Health & Human Services and reproduced by the Hobart City Council's Development and Environmental Services Division.  It is current as at 16 October 2003.

For further information call the Public Health Hotline on 1800 671 738 or visit the website at www.dhhs.tas.gov.au.