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Occupational Health and Safety Information Sheet - Legionella and Cooling Towers

Information Sheet No. 16

What is Legionella (Legionnaires' Disease)?

Legionnaires' Disease is caused by the Legionella bacteria. It is a very rare form of pneumonia (chest infection). Early symptoms are very similar to influenza. It is diagnosed from culture of the bacterium from clinical specimens (e.g. sputum) taken from patients thought to be suffering from the infection. The infection can be treated with antibiotics. However, severe cases can result in death.

Where does it occur?

Legionella bacteria are associated with water and are widespread in the environment. They are found in lakes, rivers, hot springs and other bodies of water as well as soils. Legionella may also be found in cooling towers associated with air conditioning systems and industrial processes. The temperature of water in these systems is kept between 28°C and 45°C. These conditions allow the bacteria to breed in large numbers. Optimal temperatures for Legionella growth are 25°C - 50°C. The most rapid proliferation occurs at 38°C.

How do you get Legionnaires' Disease?

Infection is 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 by drinking water contaminated with Legionella.

Who is at risk?

The disease does not affect everyone who comes into contact with the bacteria. The groups most at risk are:

  • People over 50 years of age (predominantly males)
  • Heavy smokers
  • Heavy drinkers
  • Diabetics
  • People with chronic lung disease
  • People with impaired immune systems (ie body defence mechanisms)

How is it prevented and controlled?

There is no vaccine available for the prevention of Legionnaires' Disease. This therefore increases the importance of control measures taken to prevent possible growth of Legionella in cooling towers, warm water systems and spas. These measures include regular maintenance of all systems, including chemical treatment and sampling to determine the presence of the bacterium. Because Legionella is widespread in the environment eradication of the bacteria is impossible.

The Health (Infectious Diseases) Regulations 1990 require cooling towers to be maintained and disinfected in accordance with set Guidelines and Standards (see list below).

What is Monash University doing?

Monash University is in compliance with all of the Victorian Government Regulations, Guidelines and Standards (refer list below).

Maintenance Services at each Campus of the University carry out regular maintenance checks of Cooling Towers. Cooling Towers at most campuses have been or are being fitted with an "Automatic Dosing System". This means that the towers are automatically continuously dosed with a potent Broad Spectrum Biocide (a substance which kills bacteria). On some campuses, cooling towers are additionally dosed with an alternative Biocide by an accredited outside company. This is to prevent growth of Legionella as well as the emergence of new strains of bacteria.

For all sites total bacterial counts (TBC) are performed monthly. If the TBC are elevated immediate further testing is carried out for the presence of Legionella. An independent (NATA accredited) company carries out the tests. All cooling towers at all campuses are cleaned quarterly. At Clayton, Caulfield and Gippsland the Maintenance Department initiated regular testing for the Legionella bacterium in addition to the TBC. At Clayton and Caulfield testing specific for Legionella is carried out six monthly, at Gippsland three monthly.

All new cooling towers at the University are fitted with "drift eliminators" and conform to AS/NZS 3666. Drift eliminators decrease the "fall out zone" of any aerosols formed by the cooling tower and therefore decrease the possibility of bacterial infection. In addition, all cooling towers at the various campuses are run at relatively low temperatures ranging from below 25°C - 34°C.

Although Monash University (Clayton Campus) has one of the largest numbers of cooling towers in Victoria (for a single site), no cases of Legionnaires' Disease have been reported at this campus for the past fifteen years. This is attributed to the university's maintenance program, which strictly adheres to best practice for controlling the spread of Legionella. This involves routine inspections, maintenance and testing of all cooling towers as required by the Victorian Government Regulations and Standards Australia.

Standards and Guidelines

  • Health (Infectious Diseases) Regulations 1990: Division 3- Prevention of Legionella
  • Guidelines for the Control of Legionnaire's Disease 1989 (Vic. Government)
  • Legionnaire's Disease and Cooling Towers, Information for Owners and Managers 1996 (Vic. Government)
  • Evaporative Coolers, An Operation and Maintenance Guide for Owners 1997 (Vic. Government)
  • Australian/New Zealand Standards AS/NZS 3666

For additional information, contact Occupational Health and Safety on:

May 2000