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Legionnaires' disease

The purpose of this fact sheet is to provide employers with information on Legionnaires’ disease, the risk factors which contribute to contraction and advice on risk control mechanisms.

What is Legionnaires’ disease?

Legionnaires’ disease is an infection caused by exposure to Legionella bacteria.

Legionella bacteria are very common in our environment at low levels and can be found in rivers, ponds and soil. Air conditioning cooling towers and warm water systems can provide a warm, supportive environment conducive to growth well beyond normal environmental levels. The presence of other water based organisms, such as amoeba, algae and other bacteria within these environments can provide greater nutrient levels further enhancing growth of Legionella.

Legionnaires’ disease is a type of pneumonia caused by Legionella pneumophila, one of 39 species of Legionella bacteria. It takes between two to ten days for symptoms to appear. Symptoms include malaise, headache, chills, rapid onset of high fever, cough, and other influenza-like symptoms. Legionnaires’ disease can be a life threatening disease.

Pontiac Fever, also caused by Legionella bacteria, is a milder, non-pneumonic disease which is considered non-life threatening. Symptoms are similar to influenza and recovery usually occurs within 2-5 days.

How is Legionnaires’ disease spread?

Often cases of Legionnaires’ disease can be traced to exposure to mists or airborne water droplets containing Legionella bacteria. Commonly, such mists come from air conditioning cooling towers and warm water systems, although other sources are known, including aerosols from spa baths and potting mix. (This fact sheet does not address these other sources). Legionnaires’ disease is not transmitted from one person to another.

Are some people at greater risk from Legionnaires’ disease than others?

Risk of infection is a combination of two factors – the amount of Legionella bacteria to which the body is exposed and the resistance of the individual to the bacteria. Thus it is only possible to make general statements about risk. However, risk is increased for those whose immune system is already under stress for any reason, including illness or medical treatment, such as radiation therapy. Diabetics, those suffering chronic lung, heart or kidney disease, aged persons, smokers and heavy drinkers also have some increased risk. For all of the above categories, males are more at risk than females. Fatality rates for those contracting the Legionnaires’ disease range between 5, however the rates in some outbreaks have been known to reach as high as 50%.

How can the risk of Legionnaires’ disease be reduced?

The key to reducing the risk of contracting Legionnaires’ disease is to minimise the risk of exposure to Legionella bacteria. This is achieved by effective management of air conditioning cooling towers and warm water systems and other such plant that afford optimum conditions for Legionella growth and provide a means of dispersal.

What steps can an employer take to manage the risk of Legionnaires’ disease when working through third parties?

Employers will generally contract out cooling tower maintenance functions or, where the employer is a lessee, such services will generally be undertaken by building owners/managers. In these cases, the following steps will assist employers to meet their OHS obligations under the Act.

  • Ensure there is a formal, enforceable agreement with building management/contractors (eg lease, service contract) clearly setting out maintenance and testing procedures and ensuring compliance with measures outlined in AS/NZS 3666* and SAA/SNZ HB32# or other equivalent or better standards.
  • Ensure the above mentioned agreement includes timing, content and format of maintenance reports, consistent with that contained in Section 10 of AS/NZS 3896**.
  • Implement in full, all requirements as detailed in the Comcare Approved Code of Practice on Indoor Air Quality.

What does an employer need to know about air-conditioning plant and maintenance?

In an effort to prevent the occurrence of Legionnaires’ disease, it is recommended that employers should:

  • obtain expert advice on the type of air-conditioning plant in use, its age, method of operation and any features likely to affect production and dispersal of Legionella bacteria

This step ensures the level of risk associated with the specific plant in a given location is clearly understood. Risk will vary according to age, design and manufacturer.

  • Obtain expert advice in relation to a suitable maintenance regime for the plant, with an emphasis on water quality and water treatment.

This step ensures a suitable preventative regime is developed as an effective counter against Legionella growth.

  • Obtain regular reports on all testing and any treatments undertaken by building management/maintenance contractor as part of their routine, remedial or seasonal maintenance.

Any variance on maintenance may be indicative of problems with the plant. Such information will ensure risks or matters affecting risk levels are better understood.

What are the important features of maintenance procedures?

Where suitably qualified engineers have established the need, maintenance procedures are likely to incorporate the following features.

  • Dosing involves the addition of biocides to control microbial growth, fouling, scaling and corrosion. Dosing should aim to achieve zero Legionella growth. Dosing will be a regular, preferably automatic, procedure. Dosing level and frequency may vary with seasonal changes.
  • Cleaning and de-fouling should be undertaken at least every three months, with an emphasis on cleaning prior to onset of warmer weather or after a prolonged shut down.
  • Testing is undertaken to determine the efficacy of the maintenance procedures (NOT to detect health risk). It is generally expected that routine testing will take place at least monthly.

What information should reports contain and what should employers look for?

Results of water testing should be read with a view to monitoring bacterial growth and identifying any growth patterns. Zero levels are the desired outcome. The guide below gives an indication of the level of risk experienced when tests indicate levels above zero (or <10cfu/ml, the limit of testing accuracy).

cfu: Colony Forming Units (standard scientific measure of bacteria population levels)

Should an employer be concerned about high counts of heterotrophic micro-organisms?

It is strongly recommended that if consecutive test results indicate levels above zero, maintenance should be reviewed and a determination made about the need for additional controls.

The content of a test report, made in accordance with AS/NZS 3896, should state total Legionella bacteria found in the sample, expressed as xcfu/ml water, for Legionella pneumophila, broken into serogroups or types and total Legionella non-pneumophila. (For more detail see AS/NZS 3896 and sample report attached.)

Legionella pneumophila should be the focus, especially type 1, as it is the strain most commonly associated with Legionnaires' disease, although other Legionella strains are also considered capable of infection.

Reports should also contain tested levels of heterotrophic micro-organisms expressed as xcfu/ml. Heterotrophic micro-organisms are not generally considered a direct threat to health, however, higher levels are indicative of the overall poor quality of the water environment, increasing the potential for Legionella bacteria growth.

Recent evidence points to a sometimes symbiotic, other times parasitic, relationship between some micro-organisms and Legionella. These relationships may variously:

  • disguise the presence of Legionella
  • provide protection from biocides normally effective in controlling "free-living" Legionella
  • provide for greater opportunities for amplification of Legionella

Consequently, levels of Legionella could be much higher than testing indicates and normal control methods may prove insufficient.

Comcare believes it is important to recognise the possibility of these relationships. It is important to ensure heterotrophic micro-organisms, which are a useful indicator of the general microbial population, are controlled with the same rigour as Legionella.

When viewing test reports, what levels should concern employers?

The Approved Code of Practice on Indoor Air Quality (which incorporates AS 1668.2***, AS/NZS 3666.1, AS/NZS 3666.2 and AS/NZS 3666.3) sets out specific actions required when tests indicate specific bacterial levels have been exceeded. These levels are set out below. When exceeded, employers should satisfy themselves that appropriate investigation, review and remedial action has been undertaken.

AS/NZS 3666 sets out the following responses to Legionella bacteria levels:

  • <10 cfu/ml Maintain existing procedures
  • <1000cfu/ml Investigate, review, take remedial action
  • >1000cfu/ml Investigate, review, take remedial action
  • AS/NZS 3666 sets out the following responses to heterotrophic micro-organisms:
  • <100,000cfu/ml Maintain existing procedures
  • >100,000 – <5,000,000cfu/ml Investigate, review, take remedial action
  • >5,000,000cfu/ml Investigate, review, take remedial action


These levels are for guidance only. At all times, maintenance must aim to achieve zero (<10cfu/ml) levels of Legionella. Testing is undertaken to determine the efficacy of treatment procedures, NOT to detect health risk. Testing and detection methods for Legionella can take up to 10 days. Therefore, health problems can present well before detection.

What should an employer do if reports show consistently high readings of Legionella or other organisms?

Readings consistently over 1000cfu/ml Legionella or over 100,000cfu/ml heterotrophic micro-organisms in a cooling tower, would indicate problems with:

  • maintenance procedures to manage water quality; and/or
  • maintenance of the actual physical equipment making up the tower or its ancillary parts; and/or
  • design faults/construction errors with the tower or its ancillary parts

Consultation with building owner/managers and/or contractors should commence immediately to determine the timing and type of corrective action required.

Employers must exercise their own judgement about the need for independent expert advice to supplement that from existing sources.

In relation to staff, employers are encouraged to make staff aware of concerns when there is a greater health risk due to higher bacterial levels. This would occur when readings are in excess of assumed safety levels as follows:

  • Legionella reach 1000cfu/ml; or
  • heterotrophic micro-organisms reach 100,000cfu/ml in three (3) consecutive samples, no more than one week apart, following the application of appropriate treatment protocols

In such cases, staff should be advised immediately.

Employers should also liaise with appropriate health experts to determine if further action is required to minimise risks of exposure. (See attached listing.) Such action is recommended due to the fact that little is known about what constitutes an infective dose causing Legionnaires’ disease.

Advice to staff should include:

  • broad information about Legionnaires’ disease
  • specific advice on those considered to be in high risk groups
  • the symptomatology of Legionnaires’ disease
  • advice to notify supervisors and seek medical advice when symptoms occur

What should an employer do when staff present with symptoms consistent with Legionnaires’ disease?

Staff generally should be advised of the risks associated with Legionnaires’ disease, in particular persons who are known to be in higher risk categories.

Where symptomatology consistent with Legionnaires’ disease presents in staff, they should be advised to seek immediate medical assessment of their condition with a medical practitioner.

Infection rates for Legionnaires’ disease are relatively low, around 5% of the population exposed to significant levels of Legionella develop Legionnaires’ disease.

Early symptoms of Legionnaires’ disease include:

  • high fever
  • chills
  • malaise
  • headache
  • muscle pain

These earlier symptoms then generally develop into a dry cough followed by breathing difficulty. Anyone developing such symptoms should immediately seek a medical opinion.


The incubation period for Legionnaires’ disease is from two to ten days. While tests of cooling towers and other water sources may not indicate the presence of Legionella bacteria, it should be remembered that there will be some time lapse between water sampling and the availability of associated test results. During this time it is possible that staff may have been exposed to Legionella bacteria.

In addition, little is actually known about the infective dose that is needed to cause Legionnaires’ disease in humans, thus when a high count of Legionella is detected, it is essential to carry out a full risk assessment to determine the potential risk to the staff. Factors that need to be taken into consideration are the location of the cooling tower, exposure pathway, the sero type of legionella and the various risk groups potentially exposed in and around the building containing the cooling tower.

Is there a requirement to notify Comcare?

In accordance with Section 68 of the Act, employers must notify Comcare when there is "a dangerous occurrence". This is considered to have occurred when:

  • an employee is confirmed as, or in the opinion of a suitably qualified medical practitioner, is strongly suspected of, having Legionnaires’ disease; or
  • testing readings are in excess of assumed safety levels. This would be when:
  • Legionella bacteria reaches 1000cfu/ml; or
  • heterotrophic micro-organisms reaches 100,000cfu/ml in three (3) consecutive samples, no more than one week apart, following the application of appropriate treatment protocols

The above levels are those generally accepted by Australian and international authorities as being the benchmarks to control exposure and significant risk of disease, including Legionnaires’ disease. Where testing indicates these levels have been reached, this should be notified to Comcare as "a dangerous occurrence".

Are there any other obligations employers need to be aware of?

While the primary concern of this document is to address the issue of Legionnaires’ disease as an occupational health and safety issue, Legionnaires’ disease is also a matter of concern to state and territory government public health authorities. High Legionella readings and outbreaks of the disease carry a requirement to notify authorities in some states and territories. Local government may also require reporting in some cases given their community and environmental health responsibilities. All organisations need to be aware of such circumstances as they exist in each physical location.

Other places where employers can get assistance or further advice


Fact Sheet on the Approved Code of Practice on Indoor Air Quality

Standards Australia

  • *AS/NZS 3666 parts 1-3, Air-handling and water systems of buildings – Microbial Control,
  • **AS/NZS 3896 Waters – Examination for legionellae including Legionella pneumophila
  • ***AS 1668 part 2, The use of mechanical ventilation and air-conditioning in buildings
  • #SAA/SNZ HB32 Control of microbial growth in air-handling and water systems of buildings.

ACT Department of Health and Community Care

ACT Cooling Towers and Warm Water Storage Systems Code of Practice 2000

Victorian Department of Human Services

Guidelines for the Control of Legionnaires’ Disease
Legionnaires’ Disease: Managing the Health Risk Associated with Cooling Towers

Health and Safety Executive, UK

The Control of Legionellosis including Legionnaires’ Disease

The Australian Institute of Refrigeration, Air –Conditioning and Heating (Inc.)

Application Manual: Cooling Towers No: DA17
Application Manual: Water Treatment

Health Experts

The following list of state and territory contacts who should be able to provide expert advice when there are indicators of possible Legionnaires’ disease outbreaks or increased risk of exposure of staff and customers to Legionella bacteria.

The expertise to assist in such circumstances generally resides within the health authorities of each state and territory which are listed below.

The following list was accurate at the time of print, however an organisation’s name and phone numbers may change from time to time. It is recommended that employers make a note of the name and number of the relevant authority in each physical location.

  • State/Territory Authority Phone No
  • New South Wales NSW Health, Public Health Units Listed in White Pages under Health
  • Victoria Department of Human Services
  • Environmental Health Unit (03) 9637 4126
  • Queensland Queensland Health
  • Western Australia Health Department W.A.
  • Applied Environmental Health Section (08) 9388 4967
  • South Australia Department of Human Services
  • Environmental Health Branch (08) 8226 7100
  • Tasmania Department of Health and Human Services
  • Public and Environmental Health (03) 6233 2898
  • Northern Territory Territory Health Services (08) 8999 2400
  • ACT Department of Health and Community Care
  • Health Protection Service (02) 6205 1700


Sample : Precise location from where sample is taken.

Sample No: Unique number to identify sample, given at time of collection.


Total Plate Count: Expressed as xcfu/ml. (Can also be stated as SPC, Heterotrophic Micro-organisms.)

Legionella Count: Expressed as xcfu/ml Legionella pneumophila serogroup/type 1

Expressed as xcfu/ml Legionella pneumophila serogroups/types 2-14

Expressed as xcfu/ml Legionella species non-pneomophila

Date/Time Collected: Date and time of sample collection

Date Tested: Date of actual test

(Statement containing interval between sample collection and testing < or > xxhrs, sample storage at

xdegrees C until tested. Statement that sample tested as received.)

Laboratory Reference Number: Unique number allocated to test and recording of procedure.

Testing Method: Statement containing reference to method used for testing, in accordance with Australian Standard.

Signature of person authorising test results as supplied.

Laboratory must be NATA (National Association of Testing Authorities, Australia) certified.

The contents of the sample report above is the minimum information to enable employers to interpret results of testing satisfactorily.

Further information

For further information about this fact sheet, or others in the series, please contact Comcare on the general enquiry line 1300 366 979 or by email

Page last updated: 15 Mar 2018