Last updated:
06 September 2004
1. Reason for surveillance
- To identify and control common sources of infection and transmission
- To monitor the epidemiology and so inform the development of better prevention strategies.
2. Case definition
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 NAT, or
Clinical evidence
Epidemiological evidence
Not applicable Confirmed case
A confirmed case requires laboratory definitive evidence AND clinical evidence. Laboratory definitive evidence
- Isolation of Legionella, or
- Presence 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
As with probable case. Factors to be considered in case identification
There are currently more than 45 species, but the most commonly identified in NSW are L. pneumophila, which may be found in water cooling 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. The urinary antigen test is sensitive and specific for L. pneumophila type 1. 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 10 days. Though commonly found in aquatic habitats, Legionella species are fastidious organisms, requiring specific conditions for culture in the laboratory.
3. Notification criteria and procedure
Legionnaires' disease is to be notified by:
- Hospital CEOs on provisional clinical diagnosis (ideal reporting by telephone on same day of diagnosis).
Legionella infections are to be notified by:
- Laboratories on diagnosis (ideal reporting by telephone on same day of diagnosis).
Probable and confirmed cases should be entered onto NDD.
4. The disease
Infectious agents
The Gram-negative bacilli Legionella species. Mode of transmission
Infection with L. pneumophila is caused by inhalation of contaminated aerosols. 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. Timeline
The typical incubation period is 2 to 10 days, but more commonly 5 to 6 days. 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 an chills, but not pneumonia or death, has also been reported following exposure to Legionella bacteria.
5. Managing single notifications
Response times
Investigation
On same day of notification of a probable or confirmed case of L. pneumophila, begin the follow-up investigation using the Legionnaires Disease Investigation form. Within 1 working day of notification of a probable or confirmed case of other species, begin follow-up investigation using the Legionnaires Disease Investigation form. Data enrty
- Within 1 working day of notification enter on NDD confirmed and probable cases only
- Within 1 working day of notification of the serogroup of the organism, update NDD.
Response procedure
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.
Case management
Investigation and treatment
Where cases are clustered, ensure that clinical isolates are sent to ICPMR for typing. Refer to Therapeutic Guidelines: Antibiotic for treatment options. A history of possible exposures should be sought. If the onset of the illness can be clearly identified, then ask about exposures in the 2 to 10 days before onset. However 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:
- Water cooling systems, in, for example, commercial premises such as shopping centres and clubs
- Warm water systems which supply water at less than 60°C at the usage site
- Other sources of water aerosols, e.g. vegetable mist machines
For L. longbeachae:
- Gardening activities, particularly the use of potting mix.
Education
The case or relevant care-giver should be informed about the nature of the infection and the mode of transmission. Isolation and restriction
None. Environmental investigation
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 an opportunity to check registers of cooling towers held by councils, and provide information to managers of premises while testing any suspected water cooling system. If 2 or more cases share a common exposure, potential sources should be investigated. Investigation of possible sources for a cluster may include a search for sources of aerosols that are likely to have travelled to the vicinity in which the cases were potentially exposed. Some sources of aerosols may include:
- Water Cooling Systems (WCS) both registered and unregistered
Potential WCS sources of aerosols could be identified by:
- Considering distances from the common point of exposure, building height, WCS 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 WCS selected
- Reviewing the local council's register but be aware of the likelihood for unregistered WCS in buildings in the vicinity
- Considering potential for higher health risk, e.g., where many susceptible people could be exposed
- Considering known history of poor performance / compliance.
The PHU should work with local councils to identify potential sources of aerosols. The selected WCS and its on-site records should be inspected as a minimum. WCS should be sampled if there is a serious non-compliance with the audit tool or a recent non-complying microbiological water sample. WCS should be cleaned and disinfected if there has been a serious noncompliance with the audit tool or a recent non-complying microbiological water sample and the WCS has not been cleaned within the past three months. Those WCS that require cleaning and disinfection should be re-evaluated by the PHU within 2 weeks but not within one week of cleaning or disinfection. Samples of water from the source should be sent to the Division of Analytical Laboratories (DAL) for testing for Legionella species. Positive samples should be held by DAL and matched against any human isolates. Where a spa pool(s) is implicated both the body of water and the filter should be sampled / swabbed for Legionella. Where a warm water system is implicated it should be assessed using the audit tool. For detailed information on environmental Control of Legionella contamination see:
http://www.health.nsw.gov.au/publichealth/ehb/general/microbial/microbial.html Contact management
Identification of contacts
Potentially exposed people are those who may have been exposed to the same source as the case. Consider issuing a warning to these people where a likely source is identified.
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