Follow-up/respond to all confirmed and probable cases of legionellosis irrespective of species. Determine possible exposures and consider an environmental assessment especially where more than one case of legionellosis reports a similar exposure or if a case has occurred in a healthcare or institutional setting. All cases must be notified to the appropriate State or Territory Communicable Diseases Branch.
No management of contacts is required as person-to-person transmission of the disease is likely to be very rare. Consider providing information to people potentially exposed to the same source as the case. Active case finding is undertaken when the source of infection is the workplace or an institutional setting, when the case is part of a cluster or community outbreak or if it is a travel-related case.
Legionella species are gram-negative, rod-shaped, aerobic bacteria. To 2017, at least 60 species with 70 serogroups have been identified, of which around 30 are known to cause human disease.1,2,3
In Australia the most commonly notified species are Legionella pneumophila and Legionella longbeachae. Legionella pneumophila serogroup 1 causes the majority of outbreaks.
Legionellosis is the term given for any illness caused by Legionella bacteria. The spectrum of illness ranges from a severe form of infection with pneumonia, Legionnaires’ disease, to a milder self-limiting influenza-like illness without radiographic evidence of pneumonia, Pontiac Fever.4
Cooling water system (CWS): a heat exchange system that consists of a heat generating plant, a heat rejection plant, interconnecting water recirculating pipe work and associated pumps, valves and controls, and includes a cooling tower or evaporative condenser.
Cooling tower: a device for lowering the temperature of water by evaporative cooling in which atmospheric air is in contact with falling water thereby exchanging heat. An evaporative condenser is a heat exchanger in which refrigerant is cooled by a combination of air movement and water spraying.
Hot water system (HWS): a reticulated water system that distributes or recirculates hot water (>60°C) through the majority of its branches. A hot water system (HWS) may include temperature control devices located near outlets to regulate the delivery temperature.
Warm water system (WWS): a reticulated water system that distributes or recirculates warm water through the majority of its branches at a nominal temperature of 45°C by means of a temperature controlling device.
Adapted from: Health Protection Programs. Control of Legionella in manufactured water systems in South Australia. Revised 2013. SA Health, Adelaide. Available at: SA Health website.
Legionella bacteria are found naturally in low levels in aquatic habitats and soil.
Most Legionella bacteria thrive in warm water (20°C – 45°C)5 and are often associated with CWS or WWS.
L. pneumophila grows readily in closed water systems in built environments such as inside plumbing fixtures and pipes where warm temperatures and the build-up of nutrients and microorganisms on surfaces (called biofilm) provide an ideal environment. In the absence of effective environmental management Legionella bacteria can proliferate.
L. longbeachae is often associated with garden soil, potting mix or compost. There have been no reports of L. longbeachae acquired via water systems in the built environment.
Legionella are transmitted to susceptible humans via inhalation of aerosols, dust or aspiration of contaminated water. Outbreak data suggests outbreaks that occur with L. pneumophila, are usually serogroup 1.
A variety of aerosol-producing devices have been associated with outbreaks of Legionnaires' disease, including air conditioning cooling towers, whirlpool spas, showers, decorative fountains, car washes, nebulisers, humidifiers and water misters.6,7,8 In these cases, proximity to the aerosol generator, duration of exposure, and presence in an area downstream of the contaminated device have all been found to be risk factors for disease acquisition.9
In a small fraction of hospital acquired Legionnaires' disease cases, microaspiration of colonised drinking water into the lungs has been implicated. Data supporting microaspiration of water as a major source of transmission are not convincing. There is evidence to support aspiration of contaminated water as a possible mode of transmission in certain subgroups, such as those receiving nasogastric feeding.10,11,12
Transmission of L. longbeachae associated with close contact with potting mixes and other sources has been documented but was not unequivocally demonstrated with multivariate analysis in a case-control study. The gardening environment and behavioural factors were better predictors of infection. These factors included poor gardening hygiene (lack of hand washing prior to eating, drinking or smoking while gardening) and being near dripping hanging flower pots.13
Person-to-person transmission of legionellosis is likely to be very rare. In 2016, there was a case documented of a mother who acquired the infection from her ill son.14
The incubation period during most outbreaks of Legionnaires’ disease is variable, averaging between 5 - 6 days (range 2 - 10 days), and outliers from 1 - 28 days.9 A nosocomial case with an incubation period of 63 days has been reported.15
The incubation period of Pontiac fever is from four hours to three days, with a median of about 1.5 days, although incubation periods of up to five days have been reported.9
The clinical spectrum of disease caused by Legionella sp. is broad and ranges from asymptomatic infection to a mild cough and low grade fever to stupor, respiratory failure, multiorgan failure and rapidly progressive pneumonia leading to death. Pontiac fever is the non-pneumonic form and is an acute, self-limiting influenza-like illness. The clinical presentation of Legionnaires’ disease includes fever, loss of appetite, headache, malaise, lethargy and pneumonia. Some patients may also have myalgia, diarrhoea, nausea, vomiting and confusion. Evidence of infection with other respiratory pathogens does not exclude the possibility of coinfection with Legionella sp.9,16,17Radiological findings commonly describe a patchy, unilobular infiltrate/consolidation but other appearances may occur along with the presence of pleural effusion.
Legionella are found extensively in the environment and many people are exposed but do not develop illness. People at highest risk of acquiring legionellosis in the community or healthcare facilities are18:
Other people at higher risk of acquiring legionellosis include:
Additional risk factors for healthcare associated infections include recent surgery, intubation and mechanical ventilation, aspiration of water contaminated with Legionella including nasogastric feeds and the use of respiratory therapy equipment contaminated with Legionella.19 Risks are further elevated if there has been recent plumbing work which has caused disturbance of biofilm or a prior history of nosocomial cases in the healthcare facility, given the difficulties of eradicating Legionella. 20
Legionnaires' disease is an important cause of community-acquired and hospital-acquired pneumonia with outbreaks of public health significance being reported globally.20,21 Global incidence is difficult to quantify due to inequalities of case definitions, diagnostics and surveillance systems.21,22
Most cases of legionellosis are sporadic. Cases occur more commonly among adults over the age of 50 years and men.9,16 The disease is rare in children.
In recent years, an average of 400 confirmed and probable legionellosis cases have been notified in Australia each year. In 2014 the notification rate was 1.8 cases per 100,000 population (range 1.4 – 2.2 cases per 100,000 population between 2010 and 2014) (NNDSS data). While in many countries L. pneumophila serogroup 1 is the most common causative agent, in Australia, L. longbeachae and L. pneumophila are notified in almost equal numbers. Notified species in Australia vary by geographical location, with L. longbeachae usually comprising the majority of notifications for South Australia and Western Australia while L. pneumophila has comprised the majority of notifications in Victoria and New South Wales.23
Cases occur throughout the year. Legionella accounts for between 0.5 and 5 per cent of cases of community acquired pneumonia.9,24
Prevention measures for legionellosis focus on the management of the environments in which Legionella are likely to proliferate. This includes ensuring compliance with national standards and codes of practice to reduce risk of proliferation and subsequent infection.
The objectives of surveillance for legionellosis are
All probable and confirmed cases of L. pneumophila and any clusters/outbreaks caused by other Legionella species should be entered onto the notifiable diseases database within three working days following notification.
Sporadic probable and confirmed cases of L. longbeachae and other non-L. pneumophila cases should be entered onto the notifiable diseases database within five working days following notification.
Update the serogroup information within one working day of report.
Notify the State or Territory Communicable Diseases Branch (CDB) of the case’s age, sex, onset date and geographical areas of exposure. Where an exposure occurred outside the public health jurisdiction, the CDB or appropriate Public Health Authority will also notify the relevant PHU or State or Territory.
The CDB should report to the National Incident Room cases of L. pneumophila whose likely place of acquisition was overseas (with details of identified potential exposure locations and sources, including hotels, spas, misting systems, etc.), for referral to the relevant national authority. The National Incident Room will advise jurisdictions of any specific known sites of potential exposure overseas as relevant.
An up-to-date list of case definitions can be found on the Department of Health’s website.27
The case definition is primarily intended to inform surveillance activities. Public health action may be considered necessary in patients not strictly meeting the criteria for a case.
(Effective 1 January 2013)
Both confirmed cases and probable cases should be notified.
A confirmed case requires laboratory definitive evidence and clinical evidence.
A probable case requires laboratory suggestive evidence and clinical evidence.
Table 1. Legionellosis testing 26,28-30
Early acute phase (e.g. within 3-4 days after onset) as baseline
*See also Section 14. Jurisdiction Specific Issues (NSW) for further detail on urinary antigen testing in NSW
For further details regarding testing visit:
Response for L. pneumophila cases and clusters/outbreaks caused by other Legionella species should commence as soon as possible, generally within one working day for probable or confirmed cases. Begin the follow-up investigation using the Legionnaires’ disease investigation form (Appendix 1). If case is sporadic L. longbeachae and other non-L. pneumophila species, follow-up should be carried out as part of routine duties.
The response to a notification will normally be carried out in collaboration with the case’s healthcare providers. PHU staff should ensure that action has been taken to:
Identify all movements and higher-risk activities undertaken by the case during the exposure period. Ask about exposures during the exposure period including potential workplace, social, sporting, travel, healthcare and domestic exposures in the two to ten days before onset.
For L. pneumophila and species other than L. longbeachae questions should be asked about the following exposures:
For probable healthcare associated cases:
If a case has spent their entire exposure period in a healthcare facility then intensive investigations and management of identified problems must be undertaken. If a case has spent part of their exposure period in a healthcare facility or institution investigations should still be undertaken to assess whether there is a significant risk in that facility. Factors to be considered are:
Questions should be asked about gardening activities including:
Refer to the current Therapeutic Guidelines, Antibiotic.32
The case or relevant care-giver should be informed about the nature of the infection and the mode of transmission, see fact sheet (Appendix 1).
Active case finding is not usually required except in the following circumstances:
Note, if it is a travel related case, please refer to Section 6. Communications.
Depending on the context, active case finding should include a review of all notified cases from the past three to six months seeking to identify common exposures. In an institutional setting it may need to extend to review of medical records to identify previously undiagnosed cases.
Where there is a high index of suspicion that the case’s workplace is the source of infection consider:
Case finding in implicated healthcare settings: contact the manager or the person responsible for infection control (as appropriate) and request that active surveillance for pneumonia in other residents and staff be conducted for at least ten days (maximum incubation period) after the risk is believed to have been controlled. This may be demonstrated by no detection of Legionella by a laboratory accredited by NATA for Legionella testing using an appropriate sampling regimen and level of detection.
Even when an outbreak has been controlled in a healthcare facility there should be ongoing surveillance because; while risks can be substantially reduced the source of infection cannot usually be eliminated.7
An environmental evaluation of possible sources should be undertaken for all notifications, especially if the case spent some or all of his/her incubation period in a setting such as a hospital or other institutional setting with people at increased risk of disease. The breadth of the investigation will be decided at the individual PHU level, taking the species of Legionella and local factors into consideration. For example, a notification may give Environmental Health Officers (EHOs), or those with appropriate expertise, an opportunity to check registers of air-conditioning cooling towers held by a jurisdiction, and provide information to managers of premises while testing any suspected cooling towers. The holding and use of registers may vary across jurisdictions.Identify all potential sources relevant to the species of Legionella including cooling towers and WWS/HWS, as well as potting mix or other gardening soils.
Obtain samples for analysis as appropriate. Positive samples should be held and matched against any human isolates. Sampling of potting mix and gardening soils is not normally indicated for sporadic cases of L. longbeachae infection.
Contacts of cases are not at risk of disease, unless they share the same environmental exposure.
Where more than one case of legionellosis reports a common exposure a cluster/outbreak investigation should be initiated. A single nosocomial case should be regarded as an outbreak. This includes:
For the purposes of Clause 33(1) Public Health Act 2010, this constitutes the procedures for investigating outbreaks of Legionnaires’ disease.
For environmental guidelines, see Legislation - Part 3, Division 2, Public Health Act 2010 and Part 2, Public Health Regulation 2012 on Legionella and Legionnaires Disease.
A validated urinary antigen test for L. longbeachae is available at some laboratories in NSW, including ICPMR at Westmead Hospital.
Policy Directive PD 2015_008 - Water - requirements for the provision of cold and heated water.
Appendix 1 - Legionnaires' disease fact sheet
Appendix 2 - Legionnaires’ Disease Environmental Investigation Procedures
Appendix 3 - Legionella case investigation form