Control Guideline for Public Health Units

Public health priority: Respond to probable and confirmed cases. Enter probable and confirmed cases on the state notifiable disease database within 1 working day. Respond to Legionella pneumophila on the day the notification is received, or within one working day for other species.

Case management: Interview patient or nearest relatives/friends about possible exposures. Environmental investigation of possible sources is indicated if exposures are shared by more than one case of L. pneumophila.

Contact management: Nil.

Last updated: 16 December 2014
  1. Summary
  2. The disease
  3. Risk assessment
  4. Surveillance objectives
  5. Data management
  6. Communications
  7. Case definition
  8. Laboratory testing
  9. Case investigation
  10. Control of environment
  11. Contact management
  12. Special situations
  13. Additional sources of information
  14. Jurisdiction specific issues (NSW)
  15. Appendices

1. Summary

Public health priority

Respond to probable and confirmed cases. Enter probable and confirmed cases on the state notifiable disease database within 1 working day. Respond to Legionella pneumophila on the day the notification is received, or within one working day for other species.

Case management

Interview patient or nearest relatives/friends about possible exposures. Environmental investigation of possible sources is indicated if exposures are shared by more than one case of L. pneumophila.

Contact management


2. The disease

Infectious agents

Gram-negative bacillus. Legionella species.

Mode of transmission

Infection with L. pneumophila is caused by inhalation of aerosolised contaminated water. Aerosols of less than five microns can reach the lower depths of the lungs. The mode of transmission of L. longbeachae from potting mix and other sources is less clear. Person to person transmission of Legionnaires' disease has not been documented.


The typical incubation period is 2 to 10 days, but more commonly 5 to 6 days.

Infectious period

Not applicable

Clinical presentation

Legionnaires' disease usually presents as pneumonia that can vary from mild to fatal.

Pontiac fever, a milder syndrome associated with anorexia, malaise, myalgia and headache followed by fever and chills, but not pneumonia or death, has also been reported following exposure to Legionella bacteria.

3. Risk assessment

Routine prevention activities

The prevention of L. pneumophila infection focuses on minimising the risk of the growth of Legionella in cooling towers through maintenance, water quality, education of building operators, legislation and enforcement. Warning labels about safe handling are placed on most bags of potting mix under an industry code of practice.

Threat and vulnerability

Legionnaires' disease was first identified in the United States in the mid 1970s after a large outbreak of pneumonia among war veterans in Philadelphia. Since then outbreaks have been identified worldwide. Outbreaks in Australia have been mainly caused by contaminated aerosols generated by cooling water systems (CWSs) (the aquatic environment within the cooling towers that are part of air conditioning systems on large buildings are conducive to the proliferation of L. pneumophila) and other sources of misted water such as shower heads and spa pools. Although exposure to Legionella is fairly ubiquitous, some people are at high risk for overt disease, including people with pre-existing lung disease or immune suppression, smokers and people with a history of substantial alcohol use. An ageing population and increased use of immunosuppressive therapy may increase the number of vulnerable people within the community over time.

Risk mitigation

Public health legislation in many Australian jurisdictions requires that building owners or occupiers have processes in place to minimise contamination of CWSs and warm water systems. Publicly available information about the safe use of potting mix may help reduce exposures to L. longbeachae. Notification of cases of Legionnaires' disease allows public health unit staff to identify clusters and identify and control sources of infection.

4. Surveillance objectives

  • to identify and control common sources of infection
  • to monitor the epidemiology of Legionnaires' disease and so inform the development of better prevention strategies.

5. Data management

Within one working day of notification enter confirmed and probable cases onto the notifiable diseases database. Within one working day of notification of the serogroup of the organism, update the database. Document potential exposure locations in the notifiable diseases database.

6. Communications

Notify the State/Territory Communicable Diseases Branch of the case's age, sex, onset date and geographical areas of exposure. Where an exposure occurred outside the PHU area, also notify the relevant PHU. The CDB should report to the National Incident Room cases whose exposure were overseas, for referral to the relevant national authority.

7. Case definition

Only a confirmed case should be notified.

Confirmed case

A confirmed case requires laboratory definitive evidence and clinical evidence.

Laboratory definitive evidence

  • isolation of Legionella, or
  • detection of Legionella urinary antigen, or
  • seroconversion or a significant increase in antibody level or a fourfold or greater rise in titre to Legionella.

Clinical evidence for confirmed cases

  • fever, or
  • cough, or
  • pneumonia.

Probable case

A probable case requires laboratory suggestive evidence and clinical evidence.

Laboratory suggestive evidence

  • single high antibody titre to Legionella, or
  • detection of Legionella by nucleic acid testing (NAT), or
  • detection of Legionella by direct fluorescent assay.

Clinical evidence for probable cases

  • fever, or
  • cough, or
  • pneumonia.

8. Laboratory testing

Testing guidelines

  • routine testing of patients is at the discretion of the treating doctor, however in a cluster of L. pneumophila infection, PHUs should encourage 1. urinary antigen testing of patients suspected to have Legionnaires' disease because infection will be rapidly diagnosed and the test is specific, and 2. sputum (or where available bronchial washing or lung biopsy) culture to enable matching of any isolates with any available
  • there are currently more than 50 species, but the most commonly identified in Australia are L. pneumophila, which may be found in cooling water systems, spa pools and warm water systems and L. longbeachae, which may be found particularly in potting mix and soil. Other species identified in Australia include L. micdadei and L. bozemanii.
  • most urinary antigen test kits are sensitive for L. pneumophila type 1 but some may cover a broader range of L. pneumophila serogroups and Legionella species.
  • many cases are diagnosed by serological tests, hence the diagnosis is usually retrospective. Seroconversion often does not occur until 3-6 weeks after onset.
  • cultures can take up to 14 days. Though commonly found in aquatic habitats, Legionella species are fastidious organisms, requiring specific conditions for culture in the laboratory.

9. Case investigation

Response times

On same day of notification of a probable or confirmed case of L. pneumophila infection and within one working day of notification of infection with other species, begin the follow-up investigation using the National Legionnaires' Disease Investigation questionnaire.

Response procedure

Case investigation

The response to a notification will normally be carried out in collaboration with the case's health carers. But regardless of who does the follow-up, PHU staff should ensure that action has been taken to:

  • confirm the onset date and symptoms of the illness
  • confirm results of relevant pathology tests, or recommend the tests be done, especially urinary antigen and sputum culture
  • find out if the case or relevant care-giver has been told what the diagnosis is before beginning the interview
  • seek the doctor's permission to contact the case or relevant care-giver
  • identify likely source(s) of clusters.

A history of possible exposures should be sought. Ask about exposures in the 2 to 10 days before onset. If the onset is not clear, it may be necessary to expand the time frame. Questions should be asked about the following exposures.

For L. pneumophila:

  • cooling water systems, in, for example, commercial premises such as shopping centres and clubs
  • warm water systems which supply water at less than 50°C after one minute at the point of use
  • other sources of water aerosols, e.g., vegetable mist machines, gardening spray systems, car washes, fountains etc.
  • spa pools.

For L. longbeachae gardening activities, particularly the use of potting mix.

If a L. pneumophila case has a history of exposure outside the public health unit's jurisdiction, advise the relevant public health unit.

Case management

For L. pneumophila, if not already done, encourage the clinicians caring for the case to collect specimens of urine and sputum for analysis. Where cases are clustered, ensure that clinical isolates are sent to the state reference laboratory for typing. Refer to Therapeutic Guidelines: Antibiotic for treatment options.


The case or relevant care-giver should be informed about the nature of the infection and the mode of transmission.

Isolation and restriction


Active case finding

Usually none for sporadic cases. Where a case's work place is suspected to be the source of infection, consider alerting others in the workplace about the risk and, should symptoms arise, to seek medical attention and to alert the PHU.

10. Control of environment

An environmental investigation of possible sources is not generally required after a single notification. However the decision to investigate should be made at the individual PHU level, taking local factors into consideration. For example, a notification may give Environmental Health Officers (EHOs) an opportunity to check registers of CWSs held by councils, and provide information to managers of premises while testing any suspected CWS.

Water from implicated systems should be sampled and submitted for analysis. Positive samples should be held and matched against any human isolates.

Where an epidemiological investigation points to a possible source as:

  • A CWS, then an EHO should inspect the CWS; where failures in compliance are identified, ensure that the CWS is cleaned and disinfected and that the CWS is re-evaluated within two weeks (but not within one week) of cleaning or disinfection. Unregistered CWS or warm-water systems should be reported to the local council or other relevant authority
  • A spa pool, then an EHO should inspect the spa system, sample the pool water, swab the filter for Legionella, and arrange for it to be cleaned and disinfected
  • A warm water system, then an EHO should assess the system and arrange for it to be cleaned and disinfected
  • A fountain, then the EHO should inspect the fountain, sample it and arrange for it to be cleaned and disinfected
  • A car wash using warm stored water, then the EHO should inspect the system, take samples from multiple sites, document the system diagrammatically and photographically for later analysis, and arrange for it to be cleaned and disinfected, or for the water heater to be turned off and disconnected and an alternative system to be used, depending on the risk assessment.

Expert advice should be sought on the cleaning and decontamination of water systems.

11. Contact management

Identification of contacts

Contacts of cases are not at risk of disease, unless they share the same environmental exposure.




Nil routine.

Isolation and restriction


12. Special situations


Where more than one case of Legionnaires' disease reports a common exposure (within 100 metres over a 3 month period), an outbreak investigation should be initiated. This includes:

  • carefully interviewing cases/carers about all possible exposures
  • mapping movements of cases during the exposure period
  • an urgent environmental assessment including a search for possible sources of aerosol generation that are likely to have travelled to the vicinity in which the cases were potentially exposed. Potential sources of aerosol generation may include:
    • Cooling water systems (CWS) -- both registered and unregistered
    • Fountains
    • Warm water systems
    • Spa pools
    • Car washes.

Potential CWS sources of aerosols are typically in the surrounding 500 metres of the common exposure area, but in determining the investigation area, consider:

  • distances from the common point of exposure, building height, CWS height, direction of discharge, wind direction, prevailing weather conditions at the time of likely exposure (temperature, inversion layers and relative humidity) and logistics of the number of CWS selected
  • the jurisdiction's register, but be aware of the likelihood for unregistered CWS in buildings in the vicinity.
  • potential for higher health risk, e.g., where many susceptible people could be exposed
  • known history of poor performance / compliance
  • liaising with the environmental testing laboratory regarding samples. Positive samples should be held and matched against isolates from linked cases.
  • notifying the public health unit media manager. Consider issuing a media release to encourage people with symptoms who may have been exposed to a likely source to seek medical care.
  • Initiate active surveillance by faxing GPs, respiratory and infectious disease physicians to assist in case finding; reviewing Emergency Department data for cases of atypical pneumonia; and where well defined and readily contactable exposed groups can be identified (such as a workplace), issuing a factsheet or letter to members of the group.
  • communicating the findings of the investigation to health care workers and the community
  • when outbreaks cross more than one public health unit area, the coordinator should be the public health director (or delegate) in whose jurisdiction the implicated source was found. Where interviews are required of cases who live outside the coordinating public health unit's area, the PHU for the area in which the case resides is responsible for interviewing the case, unless otherwise agreed by the directors of each PHU. Where a state-wide outbreak is identified, the coordinator will be appointed by the Director of the State/Territory Communicable Diseases Branch.

The PHU should work with local councils to identify potential sources of aerosols. Where the investigation identifies unregistered CWS or warm-water system, provide feedback to local council.

13. Additional sources of information

  • WHO 2007. Legionella and the prevention of legionell​osis
  • Control of Communicable Diseases Manual
  • Victorian DHS Blue Book
  • The environmental control of Legionella contamination: Legionella and Legionnaires Disease.

14. Jurisdiction specific issues (NSW)

Cases w​ith overseas exposures

For cases where the incubation period includes travel overseas – To help assist local health authorities identify possible sources, request if possible a travel itinerary for the relevant period, or detailed information about travel movements including accommodation, room numbers, activities and any possible water exposures. If staying with friends or relatives, request address information. Inform the case and seek approval for this information to be relayed via the National Incident Room to the relevant overseas health authorities

For the purposes of Clause 14(1), Public Health (Microbial Control) Regulation 2000, this response protocol constitutes the Legionnaires' Disease Emergency Management Plan.

For environmental guidelines, see Legislation - Part 3, Division 4, Public Health Act 2010 and Part 2, Public Health Regulation 2012 on Legionella and Legionnaires Disease.


15. Appendices

Appendix 1 - Legionnaires' disease fact sheet
Appendix 2 - Environmental Guidelines for Public Health Units: Annexes