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(see also DHS Victoria Health website www.health.vic.gov.au/environment/legionella/index.htm
Overseas information: www.cdc.gov/ncidod/diseases/Index.htm

LEGIONNAIRES' DISEASE

Legionnaires' disease is a rare form of pneumonia accounting for about 20-40 cases a year in Victoria and 200 cases nationally.

Early symptoms, which resemble those of flu, include headache, fever, chills, muscle aches and pains and generally, a dry cough followed by shortness of breath.  Other systems in the body can sometimes be affected, resulting in diarrhoea, mental confusion and kidney failure.  Legionnaires disease has a death rate of up to 20 per cent.

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 the majority of 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 man-made systems 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 20^oC and 45^oC.  These man-made 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.

What is the Incubation Period?

From the time of exposure, the disease usually takes five to six days to appear.  This incubation period can range from two to ten days.

What are the Risk Factors?

The disease does not affect everyone who comes into contact with the bacteria.  Certain groups are at greater risk than others.  These include:

Males over 50 years of age

Heavy smokers

Heavy drinkers

Diabetics

People with chronic lung disease

People with medical conditions that impair the body's defence mechanisms, for example transplant patients.

How is it Diagnosed and Treated?

Legionnaires' disease is diagnosed mainly from culture of the bacterium from clinical specimens such as sputum or from the detection of an increase in antibodies in blood.  This will require 2 specimens of blood taken 2 or more weeks apart.  The infection can be treated with antibiotics.

What are the Sources of Infection?

In reported outbreaks, the following sources have been implicated:

Cooling towers

Warm water systems

Spas (whirlpools)

Potential sources include any equipment that can produce aerosols.

Its Prevention and Control

There is no vaccine available for the prevention of Legionnaires' disease.  Control measures to prevent the growth of Legionella in cooling towers, warm water systems and spas consist of regular maintenance, including chemical treatment.  As Legionella is widespread in the environment, eradication of the bacteria is impossible.

The Health (Infectious Diseases) Regulations 1990 require cooling towers, warm water systems and public spas to be maintained and disinfected in accordance with set Guidelines and Standards (see below).

Relevant publications by the Department of Human Services:

Guidelines for the Control of Legionnaires' Disease 1989

Water Purification Standards for Public Swimming Pools and Spa Pools 1990

Legionnaires' Disease and Cooling Towers, Information for Owners and Managers 1996

Evaporative Coolers, An Operation and Maintenance Guide for Owners 1997

Cooling Towers, Information for Dry Cleaners 1997.

Potting Mix

In recent years cases associated with the use of potting mix have been reported.  In these cases Legionella longbeachae has been implicated.  Subsequent Australian studies have found Legionella species including Legionella longbeachae to be present in more than seventy per cent of samples of commercial potting mix.

The route of transmission is unclear and is under further study.  However, to minimise the risk of infection from potting mix, gardeners should take the following precautionary measures:

Open bag with care to avoid breathing in airborne potting mix dust.

Moisten the contents in the bag to avoid creating dust.

Always wear gloves to avoid transferring the potting mix from hand to mouth.

Always wash hands after handling potting mix even if gloves had been worn.

These same measures should be adopted when handling other gardening material such as compost.