Guidance for the public health management of Legionnaires' disease
Guidance for health protection teams (HPTs)

Overview

This guidance has been developed for use in Scotland, following the PHS method to produce health protection guidance, in line with the Scottish Health Protection Network (SHPN). A full methods statement is available.

In developing this guidance, the UKHSA Legionnaires' disease: guidance, data and analysis (2021) was adapted by a guidance development group (GDG) for use in Scotland.

You can download a version for printing but please regularly check the most recent version of the guidance available online is being referred to.

This guidance is primarily non-statutory. This means it is not a legal requirement to implement the recommendations made.

Where the guidance references a legal requirement – for example in relation to the Public Health etc. (Scotland) Act 2008 – this is made clear.

The guidance does not replace or override any legislative or statutory requirements.

This national guidance should be used as the primary reference document. This will promote consistency and minimise unnecessary variation in professional practice across Scotland. This guidance does not replace individual expert judgement or local response arrangements.

Any comments or suggested improvements can be sent to the PHS Guidance Team on phs.guidance@phs.scot

Intended audience

This guidance is for all professionals involved in the health protection or public health response to Legionnaires' disease cases, clusters and outbreaks.

This includes:

• health protection teams (HPTs)
• environmental health departments
• microbiologists
• epidemiologists

What the guidance covers

In scope

The guidance covers:

• the investigation of Legionnaires’ disease (LD) cases, clusters and outbreaks
• recommended public health actions for cases and clusters
• outbreak identification and response
• public health management of confirmed LD

This guidance replaces the  'SHPN Guideline on the management of Legionella cases, incidents, outbreaks and clusters in the community (2014)'.

Out of scope

This guidance does not address:

• clinical management of patients with Legionnaires' disease
• the investigation or management of Pontiac Fever (PF) and non-pneumonic legionellosis (NPL)
• the investigation or management of environmental contamination of Legionella

Background

Biology of Legionella

Legionella species are gram-negative coccobacilli with at least 20 pathogenic species infecting humans and 70 serogroups. Legionella pneumophila is the most common species to cause infection.

Legionella can be found naturally in freshwater environments, such as rivers, lakes, and soil, where they can survive and multiply. It can contaminate water systems, colonise and multiply within plumbing systems of buildings, posing public health threat.

Water temperatures in the range 20°C to 45°C seem to favour growth. Legionella may remain dormant, however, in cool water and multiply only when water temperatures reach a suitable level.

The presence of sediment, sludge, scale and other material within the system, together with biofilms, are also thought to play an important role in harbouring and providing favourable conditions in which the legionella bacteria may grow.

Sources of legionella infection are usually man-made due to the propensity of, for example, cooling towers, evaporative condensers, water systems, spa pools and hot tubs, to generate aerosols (see the section on investigating potential sources of infection).

Transmission and pathophysiology

Legionella pneumophila infection is primarily contracted through the inhalation or aspiration of aerosols from a source of water containing Legionella bacteria.

The infection can lead to a severe bacterial pneumonia known as Legionnaires’ disease.

The disease is not transmitted person-to-person.

Incubation period

Legionella infection has a median incubation period of six to seven days, with most cases experiencing a two-to-ten-day incubation period. However, it can range from one to 19 days.

In contrast, the median incubation period for PF is two days, with a range of one to three days after the exposure.

Clinical presentation and risk factors

Most people exposed to Legionella do not develop Legionnaires’ disease (LD).

LD cases, however, occur more frequently among individuals from the following risk groups:

• people aged over 50 years
• men
• smokers
• people with underlying medical conditions – for example, heart disease, chronic obstructive pulmonary disease or diabetes
• people who are immunocompromised

The initial symptoms of Legionnaires’ disease are:

• commonly:
  • flu-like symptoms
  • fever
  • dry or slightly productive cough, progressing to pneumonia
• less commonly:
  • diarrhoea and vomiting
  • confusion and memory problems

Fatality rate for LD is about 10% but it varies between 1 to 30%, based on underlying conditions and other factors.

Environmental factors

Legionellae can inhabit man-made water systems and reproduce quickly, depending on factors such as changes in temperature, climate and rainfall.

Consider that:

• there is a high concentration of nutrients and impurities such as other microorganisms or corrosion in the water system which will either act as a nutrient source or will provide a protective haven for these waterborne pathogens 
• water is stagnant within the system, where biofilm can develop and provide a protective environment from chemical and physical treatment of the water system

The conditions favoured by the factors mentioned above are usually created in badly designed or poorly maintained water systems, but they might also be found in well designed and well-maintained water systems.

Legionellae found in such conditions can quickly multiply, spreading throughout the water system, particularly in water temperature between 20°C and 45°C. Some Legionella species – for example, Legionella longbeachae – can survive and multiply in compost under certain conditions, particularly when the compost is kept moist and at temperatures conducive to bacterial growth.

Epidemiology

The majority of Legionnaires’ disease (LD) cases appear to be sporadic, but clusters and outbreaks are frequently detected.

Depending on the source, an outbreak can develop quickly resulting in hundreds of cases. However, prompt investigation of potential sources may help to minimise public health risks.

Approximately 40 to 60 cases of LD are reported each year among residents of Scotland, and approximately 5% of cases are fatal.

Cases occur throughout the year, but a seasonal pattern is observed with many more cases reported with onset of symptoms over the summer months (June to October).

Consider cases might be driven by travel and exposure to possible community sources of infection, especially during the peak travel seasons.

Each year, Public Health Scotland (PHS) publishes a report on the epidemiology of LD in Scotland.

View the most recent Legionnaires’ disease in Scotland report.

Notification and reporting

Statutory notification

Legionella genus is a notifiable organism under the Public Health etc (Scotland) Act 2008.

PHS has conducted enhanced surveillance of Legionnaires' disease alongside the Scottish Microbiology Reference Laboratory (SMiRL) since 1994.

Laboratories must:

• verbally notify the local health protection team (HPTs) when Legionella spp. has been identified in a human sample
• record in Electronic Communication of Surveillance Scotland (ECOSS) within 24 hours after confirmation

Reporting confirmed Legionnaires’ disease (LD)

Reporting procedures for confirmed LD, and the relevant form, can be found in the national enhanced Legionella surveillance form.

PHS co-ordinates the collection of enhanced surveillance information of LD in residents of Scotland.

Enhanced surveillance form must be completed and submitted to the PHS (the Respiratory Bacterial Pathogen team by email at phs.legionella@phs.scot) on the confirmation of a case.

Reporting timely and accurate details on cases within 24 hours of confirmation is important, as the PHS Respiratory Bacterial Pathogen team can:

• support the identification of potential outbreaks or clusters across NHS boards
• assist in identifying potential sources
• liaise with international public health authorities as necessary for reporting travel-associated cases

Case definitions

Legionnaires’ disease (LD)

Following notification of a case, the diagnosis should be reviewed to ensure that it meets the case definition.

Probable case of LD (following declaration of an outbreak only)

A case with a clinical diagnosis of pneumonia but no microbiological evidence for confirmed LD infection (above) can be considered a probable LD case where the location and onset date(s) meet the outbreak case definition for the exposure category.

• Public health action can be initiated while waiting for test results from Scottish Microbiology Reference Laboratory (SMiRL) as the legionella reference laboratory. If the findings from SMiRL do not support the diagnosis of Legionella infection, then the case will be excluded from further public health action.
• Antigens for Legionella pneumophila in urine may not be detected in all LD cases and, therefore, other diagnostic methods may need to be considered on an individual case basis.

Confirmed Case of LD

A clinical or radiological diagnosis of pneumonia with laboratory evidence of one or more of the following:

• isolation (culture) of Legionella species from a respiratory specimen
• the presence of Legionella pneumophila antigen in urine specimen
• detection of Legionella spp. nucleic acid (e.g, by PCR) in a lower respiratory tract specimen (e.g, sputum, bronchoalveolar lavage (BAL))

Definitions in relation to exposure and settings

Definitions of a cluster and of an outbreak

See the section on clusters and outbreaks.

Pontiac Fever (PF)

Following declaration of an outbreak only

PF will be only be investigated in the context of clusters and outbreaks.

While investigating an outbreak, several criteria are considered.

• Clinically, PF is characterized by a flu-like, self-limiting illness without pneumonia.
• Laboratory confirmation is challenging due to the lack of specific tests, however, the following tests may be useful if feasible:
  • isolation (culture) of Legionella species from a respiratory specimen
  • detection of Legionella spp. nucleic acid (e.g, by PCR) in a lower respiratory tract specimen (e.g, sputum, bronchoalveolar lavage (BAL))
  • Legionella pneumophila antigen in urine specimen
• Exposure to a source of Legionella bacteria confirmed by the isolation of Legionella from environmental specimens, such as contaminated water systems or aerosols.

Clinical samples

The presentation of Legionella infection cannot be distinguished clinically from that of pneumonia due to other causes, and special diagnostic methods are required.

However molecular testing of lower respiratory tract samples for Legionella species and L. pneumophila can be incorporated into a molecular screening test (polymerase chain reaction (PCR)) to detect a range of micro-organisms at the local diagnostic laboratory.

All clinical samples should be forwarded to SMiRL for confirmation and legionella typing.

For information on appropriate specimens, refer to pages 9 and 19 in the Scottish microbiology reference laboratories user manual. 

Legionella infections where the diagnosis is made using only serological methods or direct immunofluorescence no longer meet the case definitions for the purposes of public health action or surveillance.

Environmental investigations and sampling

EHO, Water and Environmental (FW&E) microbiology laboratories provide advice on sampling and testing for legionella bacteria.  

Some of the microbiology diagnostic labs are accredited for Legionella water testing and will do so in response to suspected healthcare cases.

Search for an accredited UKAS laboratories for Legionella testing.

Environmental sampling is recommended whenever possible to assist public health action. The decision to sample is a result of a public health investigation.

This will consider the following:

• the degree of certainty of the suspected source
• the development of the incident
• the urgency of eliminating any potential source

The sampling officer should be appropriately trained and equipped. In some circumstances it may be appropriate for a member of EHO staff who is suitably trained to assist enforcing authorities.

Each sampling exercise must be subject to an individual health and safety risk assessment before commencement. Sampling should be carried out with due consideration of BS7592: Sampling for Legionella Bacteria in Water Systems 2022.

Water and environmental samples taken as part of the investigation of a case of Legionnaires’ disease should be submitted to the local FW&E microbiology laboratory in line with current procedures and protocols. At all stages, the chain of evidence must be maintained.

Scottish FW&E microbiology laboratories provide expert advice and testing of environmental samples, and can provide support and training around sampling.

Enforcement

The local authority (LA) may be assuming two roles:

• public health investigation
• enforcement under Health and Safety at Work legislation

LA Environmental Health Officers (EHO) are authorised to carry out sampling of premises where there is a work activity and/or a statutory duty of care owed to the occupiers of a property.

There is no prescriptive power of entry and statutory requirement for domestic sampling of LD cases. However, EHOs may undertake domestic sampling as part of their wider public health investigatory powers under the Environmental Protection Act, 1990.

Other powers are available where a property is owned by a landlord and statutory interventions are required.

The lead authority for the purposes of health and safety will be determined by the Health and Safety (Enforcing Authority) Regulations 1998.

In the case of a LA controlled premises or site, this will be the Health and Safety Executive (HSE). Where this is the case, LA officers may assist the HSE in their investigations, however, relevant decisions must be taken by the HSE, not LA officers.

In cases where the HSE is the lead authority for health and safety issues, the LA will always still retain its public health responsibilities. LA officers are authorised under the Environmental Protection Act 1990 to enter certain premises to determine if there is a statutory nuisance and may take samples for this purpose.

While HSE will co-operate with sampling, HSE inspectors are not required to sample as microbiological evidence is not required to support enforcement action.

However, if samples are obtained, HSE will be interested in the results. There is therefore no need for HSE to authorise LA officers to accompany them to take samples.

The sampler, if not a LA officer, should obtain samples after consultation with the LA officer to ensure that an appropriate sampling strategy has been adopted.

Environmental investigation

Local HPTs may request sampling from a few different sites during a public health investigation.

Appropriate action must be taken to reduce the risk to the public from suspected sources pending any environmental investigation.

Information may need to be disseminated over a wide area to ensure systems are shut down but not immediately disinfected (if sampling is to be carried out).

Systems which cannot be shut down without severe consequences may have to be disinfected prior to sampling. Disinfection should take place as soon as possible after any sampling. Disinfection is the responsibility of the relevant duty holder.

In a scenario where disinfection or temperature control has been implemented before sampling for legionella test by culture, then a discussion with the FW&E laboratory should be made to consider analysis by PCR.

Health and safety considerations

Prior to sampling, a health and safety risk assessment of the sampling activity must be carried out.

This will include how to take the samples with due consideration of the health, safety and welfare of sampling officers and other persons when sampling is carried out.

Sampling staff must be trained in off-site working and should be familiar with their employer’s off-site and dynamic risk assessment arrangements.

Sample collection

Disposable single use sample consumables such as bottles, swabs and other materials used to facilitate sampling, such as cool boxes and sample bags, should be stored appropriately, in date and without extraneous contamination.

Any water or environmental sample collected provides a snapshot of the microbiological quality of the system at the time of sampling. Sampling should only therefore be carried out by experienced persons.

Transport

All water or environmental samples for legionella examination should be stored at an ambient temperature (approximately 20°C), in the dark, and returned to the laboratory for testing as soon as possible (less than 24hours).

If samples are not transported by sampling officers, a courier should be pre-arranged through SMiRL in advance.

Further details of appropriate sampling points are given in Approved Code of Practice and Guidance: L8 (HSE 2013).

Laboratory testing and interpretation

Environmental investigation samples may be tested for legionella by culture and/or PCR.

Examination by quantitative PCR for the detection of Legionella in water and other environmental samples is available as a national service only where a need is agreed by the local incident control team.

Investigation for potential sources of infection

The decision to investigate a potential source should be based on the risk to those who are exposed to it, in conjunction with local protocols and resources.

Investigations should be initiated simultaneously on those sources considered to be of high risk.

The 14-day exposure history, starting from the second day before the onset of symptoms, should be used to identify and investigate potential sources of infection.

Most cases will have multiple potential sources, and each should be considered individually on their likely risk to the public.

Cases are typically categorised for source of infection by their most likely potential source of infection, as identified by exposure history or any epidemiological link between the case and potential source.

They are classified as either:

• healthcare-associated
• travel-associated
• community acquired

These categories are not mutually exclusive, and any exposures should be investigated if thought to be a risk.

Potential sources of infection in PF will be investigated only in the context of clusters or outbreaks.

Investigation and management of single cases of LD associated with healthcare settings

Definitions

It can occur in individuals who have had significant exposure to healthcare associated premises during 2 to 14 days before the onset of symptoms.

This includes (for some or all of the two to 14 days prior to the onset of symptoms for LD):

• primary care centres
• hospitals
• dentist clinics
• hospices

The terms 'probable' and 'possible' might be used while investigating LD in hospitals or in healthcare facilities only to:

• indicate the likelihood of infection in those settings
• facilitate decision-making for further action

However, they don’t change the primary definition of confirmed LD case.

This section does not relate to LD cases in registered care or nursing homes.

For community-acquired cases, refer to investigation and management of community-based settings associated with single cases of LD.

Public Health management of outbreaks in healthcare settings

Outbreaks in healthcare settings have high mortality rates, due to the presence of vulnerable groups such as elderly and/or immunocompromised individuals.

Rapid investigation of a case associated with a healthcare setting and prompt institution of remedial measures where necessary is essential to minimise the likelihood of an outbreak occurring.

Find out more information in the Healthcare Infection Incident Assessment Tool (HIIAT).

Where a healthcare-associated case is identified, the HPT should:

1. contact the Infection Prevention and Control Team (IPCT) and Infection Control Doctor (ICD)
2. report to ARHAI via local board IPCT (using outbreak reporting tool)
3. inform the Respiratory Bacterial Pathogen Team, who will be able to provide:
   • advice to HPTs on the response to individual cases
   • historical context through national database analysis to identify previous cases and/or incidents associated with the healthcare facility

Incident Management Team (IMT)

Based on the management of public health incidents guidance, the CPHM (or infection control doctor (ICD) if a nosocomial incident) confirms that an incident, cluster, outbreak or nosocomial infection exists or a Legionnaires' disease death has been identified at post-mortem.

The CPHM (or the ICD) then activates a PAG or IMT to manage and further investigate the incident. The overall purpose of this is protecting public health and preventing further infection.

The IMT should be aware that the information may be used by other agencies for a variety of other purposes.

These include:

• public enquiries
• prosecutions
• freedom of information requests
• audits

Members of the IMT can be (but are not limited to):

• Consultant of Public Health Medicine (CPHM) or Infection Control Doctor if nosocomial (IMT Chair)
• SMiRL
• Health Facilities Scotland (HFS)
• Antimicrobial Resistance and Healthcare Associated Infection (ARHAI) Scotland
• Commissioning and Facilities Strategic Business Unit of NHS National Services Scotland (NSS)
• Healthcare Environment Inspectorate (HEI)
• Environmental Health Officer(s) from the relevant local authorities
• Health and Safety Executive (HSE)
• clinicians
• local diagnostic microbiologists
• media spokesperson
• IPCT
• hospital team
• representative from the Care Inspectorate
• a specialist Health and Safety Investigation Unit (HSIU) from COPFS

Risk assessment

Risk assessment should follow the principles set out in the management of public health incidents guidance.

It should consider the:

• individual’s time spent within the premises
• premises’ previous associations with LD cases

Consideration should be given to results of most recent routine Legionella testing and any known water safety issues in the healthcare premises.

The identification and assessment of potential sources of infection within the healthcare premises should consider:

• using the 2 to 14 day history of the case
• identify any potential sources of exposure within the premises – more specifically the hot and cold water systems and other associated equipment, such as:
  • assisted baths and showers
  • evaporative condensers
  • nebulisers and respiratory equipment
  • water features
  • humidifiers

As a priority, potential sources within the healthcare premises should be risk assessed to establish the potential for legionella colonisation and infection.

The risk assessment should:

• consider the nature and condition of the water system
• determine whether control measures are in place and effective
• identify any areas of high risk, for example, where systems with stored or recirculated water have the capacity to produce aerosols
• review the susceptibility of any person(s) exposed to these aerosols
• identify areas not in consistent use and no regular flushing regime is in place

Prospective case finding

Based on the risk assessment of the (probable or possible healthcare-associated) case, clinicians within the facility may be alerted to cases of LD associated with the hospital or healthcare premises.

As pneumonia is a common clinical diagnosis and legionella testing is not always undertaken in such patients, raising awareness among clinicians is likely to assist in early diagnosis and improved patient outcomes.

All healthcare facilities should have an established Water Safety Group by healthcare facility management that meets regularly to review:

• management strategies
• written scheme
• incidents
• any sampling or monitoring results
• actions to be taken based on water safety for healthcare premises guidelines – refer to Scottish Health Technical Memorandum: water safety (SHTM 04-01)

The Water Safety Group is not limited to but should include:

• a responsible person (related to Legionella) and their deputy
• an infection control doctor or nurse
• a consultant medical microbiologist
• a representative from the estates department
• other identified individuals or stakeholders

If an incident team is not convened, a member of the local HPT staff may liaise with the water safety group during case investigations to discuss relevant issues.

The existing water safety plan, building schematics and maintenance records should be reviewed and considered as part of the risk assessment, as should any results of previous legionella sampling.

Environmental microbiological investigations

For probable healthcare-associated LD, environmental samples should be taken from each of the potential sources identified without delay, prior to implementation of control measures such as disinfection.

However, for both probable and possible healthcare-associated LD, a decision to take samples should be taken according to the PAG recommendation and risk assessment.

Implementation of control measures

It is not necessary to await the results of sampling before undertaking control measures, particularly if inadequacies have been found in the management of water systems, medical equipment or cooling towers or evaporative condensers including monitoring records. For more information, refer to Legionnaires’ Disease: The Control of Legionella Bacteria in Water Systems.

Assurance should be sought that the hospital/facility has implemented the necessary control measures promptly and that their effectiveness is being monitored. Furthermore, assurance should be sought that ongoing control measures and remedial actions are ongoing and that a sampling schedule is in place to monitor and verify the parameters, including legionella counts, identified in the water safety plan.

Investigating other potential sources

In addition to investigating the presence of Legionella in water associated with the healthcare facility, other sources should be considered based on the PAG advice (particularly the SMiRL and ARHAI members).

As healthcare-associated Legionella infection is a significant potential risk to patient safety, it is essential that actions within the premises are not delayed while other exposures are investigated.

Situations where Legionellae have been identified in water systems in healthcare facilities without any known cases – that is, where routine sampling has identified high legionella counts – should be managed by the healthcare facility in accordance with their policies.

Advice for HPTs is available in:

• Responding to the detection of Legionella in healthcare premises: guidance for PHS health protection teams
• Scottish Health Technical Memorandum: water safety (SHTM 04-01)
• relevant SHTM and HSE guidance

Communications

A single case of healthcare-associated LD may attract media attention, so early consideration should be given to the development of an appropriate media handling strategy, jointly by the healthcare facility management and the local HPT.

If there is any history of previous cases associated with the healthcare premises, the situation should be reviewed to determine if this meets the criteria for a healthcare-associated cluster as described in investigating clusters and outbreaks.

Unless a microbiological and epidemiological link is established between the case and the healthcare premises, potential community exposures should still be considered, and the case investigated as community acquired.

Investigation and management of single cases of LD associated with community-based settings

Definition

A community exposure should be considered for all cases with the exception of those that have been in a healthcare facility or abroad for the entire incubation period.

Identifying potential sources

The local HPT, in conjunction with the environmental health officers (EHOs), should identify potential sources and exposures from the case’s 14-day history as reported on the surveillance form.

Carrying out a public health risk assessment is useful to prioritise the investigation of potential sources.

A public health risk assessment differs from a risk assessment of a water system or potential source, as it considers the possibility of exposure and risks to public health.

For example, a poorly maintained cooling tower may be considered to pose a greater public health risk than a contaminated household water system, as it is likely to expose more individuals. However, investigations into a domestic water system may still be appropriate, to exclude it as a potential source of infection.

Care facilities

If the case is linked to a residential care or nursing home, the HPT should notify:

• the enforcing authority for health and safety (either the HSE or LA EHO) – for more information, refer to Health and Safety (Enforcing Authority) Regulations 1998: A-Z guide to allocation
• the Healthcare Environment Inspectorate
• the care home management or owner – they should notify the Care Inspectorate

The regulator may request to review the care or nursing home paperwork relating to the institution’s:

• Legionella control protocol (written scheme)
• risk assessments
• system monitoring records including microbiological results

If there are concerns about water safety, further investigations such as site visit and environmental sampling may be necessary.

Case finding

A search should be made by the HPT for any linked cases previously reported in the last six months to the HPT and the PHS Respiratory Bacterial Pathogen Team, to rule out a cluster or outbreak.

It is suggested that a possible cluster should be considered where reported cases are resident or work within two to six kilometers (pragmatic approach) of each other and with symptom onset within a six-month period.

If the source of infection is known, the case investigation will commence within a radius of two kilometers and can be expanded up to six kilometers as required.

If the source is unknown, areas with high case concentrations (hot spots) will be targeted, initiating an investigation within a radius of two kilometers and gradually expanding to six kilometers to facilitate the identification of the infection source.

Upon receiving the completed national enhanced surveillance form, the PHS Respiratory Bacterial Pathogen Team will:

• conduct a search for cases that are clustered in time and location
• notify local teams where any such clusters are identified

Workplace

Where a suspected source is identified at a case’s workplace, enquiries may be made about the incidence of any respiratory symptoms amongst other employees at the workplace within one month prior to case onset, with due consideration to patient confidentiality.

Risk assessment of potential source

Following identification of potential sources and their priority for investigation by the public health risk assessment, a risk assessment review and inspection of the condition of suspected source(s) should be carried out based on the principles set out in the management of public health incidents guidance.

The section on community clusters and outbreaks of LD provides further information on investigating:

• cooling towers
• spa pools
• domestic water systems

Microbiological investigations of potential sources

Appropriate sampling of suspected sources should be conducted based on the risk assessment. However, domestic environmental sampling related to sporadic L. longbeachae cases is not routinely required.

Guidance on environmental sampling can be sought from the IMT or SMiRL, who should be informed before any samples are taken and sent to them.

• The PHS Respiratory Bacterial Pathogen team request that HPTs submit results of any environmental sampling linked to investigation of cases to ECOSS and phs.legionella@phs.scot
• EHOs require to implement suitable and sufficient risk assessments for the Legionella exposure to individuals undertaking any sampling to identify the potential source.

Investigation and management of single cases of LD associated with travel (UK and abroad)

Definition

Staying in travel accommodation is a risk factor for LD.

Hotels, premises, cruise ships, campsites and other accommodation sites can pose a high risk for legionella as they often have complex water systems and may remain unoccupied for long periods or be used during warmer temperatures or seasons.

Travel history

For all travel-associated cases (UK or abroad), a detailed history of all travels required, as detailed in the national surveillance form.

This includes:

• travel dates
• full names and addresses of accommodation
• room numbers
• use of facilities such as showers, swimming pools or spa pools
• any activities, excursions or day visits
• any exposure to other potential sources such as ornamental fountains and car washes

Full details of the travel history of confirmed case should be sent to the PHS Respiratory Bacterial Pathogen team which will report the case to the International Health Regulation National Focal Point (IHRNFP) for reporting to the country of travel, as appropriate.

Investigation and risk assessment

Where the case has not been abroad for their entire 2 to 14 day incubation period in case of LD, exposure to other, more local, sources should also be considered and where necessary investigated.

If a case has made single or repeated daytime visits (with no overnight stay) to a location with a potential source, investigation of this site should be considered and, if required, discussed with the PHS Respiratory Bacterial Pathogen team.

If the case is associated with travel to an accommodation site within the country, a public health risk assessment needs to be undertaken to determine if an investigation of the site may be warranted.

Where the case has visited an accommodation site outside of their area of residence, the local HPT pertinent to the case should inform the team(s) or local health board(s) that are local to the accommodation site(s) visited by the case. HPTs receiving this information should alert the relevant local enforcement agencies.

Other potential community sources the case was exposed to during their stay should be investigated in the same way as a community acquired case.

Investigating clusters and outbreaks

Every individual case of LD has the potential of being the first case in a cluster or an outbreak.

Outbreaks can evolve rapidly so urgent investigation is necessary.

Guidance on the importance of early recognition of potential infection incidents is outlined in the:

• management of public health incidents guidance
• chapter 3 of the National Infection Prevention and Control Manual (NIPCM) – healthcare infection incidents, outbreaks and data exceedance (provides a guide to IPCTs and HPTs in the incident management process within care settings)

Definition of a cluster of Legionnaires' disease

Following investigations, a cluster may be found to be sporadic, coincidental cases that are close in time and location. Conversely, further evidence may point towards a common source, suggesting an outbreak.

If further cases arise, following the initial identification of the cluster, the cluster definition should be reviewed to determine whether the developing situation still fulfils the definition or reaches the criteria for an outbreak.

A case may be excluded from a cluster if there is strong epidemiological or microbiological evidence of a link to an alternative source (a domestic exposure). It is suggested that local HPTs contact the PHS Respiratory Bacterial Pathogen team to discuss if such exclusion is applicable for specific cases.

The history of 14 day in LD must be reviewed as a whole, as exposures identified from this period may determine that a case is included in more than one exposure-specific cluster category. For example, a case may be included in both a community cluster and a healthcare associated cluster.

Exposure-specific definitions for detection of clusters of Legionnaires' disease

Definition of an outbreak of LD

Exposure-specific definitions for detection of outbreaks of Legionnaires' disease

Two or more cases of LD meeting the criteria for any type of cluster (as in exposure-specific definitions for detection of clusters of Legionnaires' disease), with an interval of no more than 28 days between onset dates of consecutive cases and one or more of the following:

• isolates from clinical

and

• environmental specimens are indistinguishable using a highly-discriminatory microbiological method (e.g. sequence-based typing) for at least two cases

or

• isolates from respiratory specimens from at least 2 cases are indistinguishable using a highly-discriminatory microbiological method (e.g. sequence-based typing)

or

• strong epidemiological evidence for link(s) between all cases (for example, a common workplace)

For the end of an outbreak, please refer to the end of outbreak section.

Initiating the investigation of clusters and outbreaks of LD

Unless otherwise specified in the guidance here, the process for investigating clusters and outbreaks is broadly similar.

The main differences will relate to the:

• urgency
• commitment of appropriate resources
• communications approach

The CPHM activates a PAG or IMT to manage and further investigate the incident, with the overall purpose of protecting public health and preventing further infection.

The IMT should be mindful that the information may be used by a other agencies for a variety of other purposes, including:

• public enquiries
• prosecutions
• Freedom of Information (FOI) requests
• audits

Initial investigations

For the purposes of this section, references will be made to an outbreak when detailing the process required for its investigation and management. Similar principles may be used for the investigation and management of clusters, depending on the situation at hand.

Following declaration of an outbreak, investigations should begin immediately during the 24 hours after the outbreak declaration. Information on cases and exposures should be reviewed to consider and generate an initial hypothesis.

Risk assessment

An initial public health risk assessment should be performed to make a decision on declaring an outbreak.

In an incident or outbreak of legionellosis, the key questions are:

• what is the likelihood of a population continuing to be exposed to Legionella?
• what is the potential impact on health?

Answering these questions requires an assessment of the risks to public health.

This assessment should be derived from interpreting the collated findings from the epidemiological, microbiological and water systems investigations and reflecting on how these compare to the findings from previous similar episodes.

The assessment will guide the definition and prioritisation of control measures and what to communicate to the public, especially those who may have been or could continue to be put at risk. It will provide a framework for evaluating the impact of control measures and identifying whether the risks to health could recur.

Epidemiological investigation of an outbreak of LD

The established IMT or PAG should ensure that the appropriate epidemiological investigations are carried out as part of the overall investigations, which will include, when required:

• developing case definitions
• case finding
• reviewing descriptive epidemiology
• conducting appropriate epidemiological studies
• environmental and bacteriological investigation
• hypotheses review
• control measures

Develop case definitions

A case definition, specific to the outbreak being investigated, should be developed to include or exclude cases from the investigation.

For example, if a common L. pneumophila subtype is identified amongst cases, this may be incorporated into the case definition. Each case should be reviewed against this case definition.

Cases that are close, but do not quite meet the case definition, should be recorded in case they become relevant at a later stage of the investigation.

Here is a template case definition for an outbreak of LD:

Case finding

The IMT should outline measures for identifying individuals who meet the outbreak case definition.

This may include providing information to local health care professionals about the outbreak and appropriate clinical testing.

The IMT should review and update the outbreak-specific case definition at regular intervals and whenever new information becomes available.

Descriptive epidemiology and hypothesis generation

Gathering as much information as possible on the cases to generate a hypothesis and identify potential sources, for example, a specific cooling tower (refer to the environmental investigations and sampling section) being the source of infection, is an essential part of an outbreak investigation of LD.

This may involve re-interviewing cases with a trawling questionnaire tailored to the area of interest to narrow down potential sources and to identify new potential sources that may previously have been overlooked.

Spatial analysis methods may be able to provide further descriptive epidemiology.

In this case, the PHS Respiratory Bacterial Pathogen Team can be contacted for further advice.

Environmental investigations and sampling in clusters and outbreaks

A dynamic risk assessment of possible sources should be undertaken.

The condition of suspected sources should be checked, and maintenance records and previous sampling results reviewed.

The public health impact of various sources should be considered within the risk assessment and IMT meeting and used to prioritise investigations.

The environmental investigations and sampling section provides further information.

Microbiological investigation

Urine specimens should be collected from suspected cases for urinary antigen testing and respiratory samples collected for legionella culture and/or PCR to enable sequence-based strain typing.

From an environmental perspective, samples should be collected from sampling points indicated by the risk assessments of potential sources. The SMiRL should be consulted and culture analysis carried out as a minimum.

It is important that both clinical and environmental isolates are obtained for epidemiological typing to provide evidence to confirm (or exclude) any links between cases and potential sources.

Hypotheses review

Use available information collected during the investigation to assess support for a specific hypothesis, for example, a specific cooling tower being the source of infection.

The IMT should consider the need for an analytical study to confirm or refute the hypothesis relating to source(s) and transmission.

Control measures

Emergency control measures should be determined by the IMT and implemented, and a record should be made of actions taken and the subsequent results.

While protection of public health remains the highest priority, every effort should be made to undertake environmental sampling prior to control measures being taken.

Additional considerations for for investigating clusters and outbreaks of LD in relation to exposure and settings

Healthcare-associated clusters and outbreaks of LD

As with the investigation of single healthcare-associated cases, the relevant health board will usually lead the IMT to investigate clusters and outbreaks of LD within healthcare premises.

Risk assessments, investigations, case finding and emergency control measures should be undertaken with urgency to protect the vulnerable population housed within the healthcare premises.

Healthcare-associated outbreaks are particularly likely to attract media interest, and a communications officer should be included in an IMT.

It is important that communication statements are prepared and reviewed regularly as the situation develops and the investigation proceeds. A single multi-agency statement should be agreed upon where possible.

The PHS Respiratory Bacterial Pathogen Team and the Communications Team at PHS should be made aware of progress of the outbreak and investigations.

Community clusters and outbreaks of LD

Community clusters can be challenging to investigate, as the only link may be proximity of the cases in time and location.

It is possible that further investigations into clusters of cases, such as the use of trawling questionnaires, may identify epidemiological links that were not initially identified.

If cluster investigations fail to identify evidence of a common source despite investigations, the IMT may decide to suspend investigations based on an assessment of ongoing risks to public health.

It is very important that lower respiratory samples are obtained wherever possible from the cases as the typing data is a key evidence-based method by which a case can be linked to a potential source or to other cases, thus indicating that an outbreak exists, or if it is a cluster of sporadic cases.

For spatial analysis tools and methods that may help to identify if an outbreak is occurring refer to the UKHSA guideline.

Cooling towers

Cooling towers are potentially a high-risk source of Legionella, with the capability to disperse aerosols over a wide area (up to six kilometers radius has been reported in some outbreaks).

Under the Notification of Cooling Towers and Evaporative Condensers Regulations 1992, owners and operators of cooling towers or evaporative condensers are required to register a cooling tower or evaporative condenser with the relevant local authority.

• Local authority EHOs or the HSE may inspect cooling towers periodically (refer to Health and Safety (Enforcing Authority) Regulations 1998: A-Z guide to allocation, and the section on roles and responsibilities.
• Operators should maintain detailed records of the monitoring, treatment regimes, and records of any legionella sampling results.

For further information on the prevention of Legionella in cooling towers see the HSE Legionnaire's disease technical guidance - Part 1: Evaporative cooling systems.

Spa pools and hot tubs

Spa-pools and hot tubs are a recognised source of diseases caused by infectious agents including the organism that causes Legionnaires' disease.

It is important to note that spa pools have been linked to cases when on display in public areas, as well as through conventional use – see the investigation for potential sources of infection section.

Further advice on effective ways to safely manage and control spa-pool systems is available in the HSE guide for the control of legionella and other infectious agents in spa-pool systems.

Domestic water systems

The term 'domestic' water systems is not restricted to within the case’s home.

It includes any type of domestic water system (such as the communal water system in a block of flats) that the case may have had contact with:

• socially
• at work
• in any other public building, for example, a leisure centre

Taps, showers and toilets are common outlets that produce aerosols, but there may be water features or other equipment that may result in the dispersal of aerosols.

Sampling of water systems that are within the cases’ home is not always a priority as it has limited public health benefit. However, sampling of the cases’ home can be useful to exclude cases from a cluster or an outbreak and may be advisable in certain circumstances, especially when communal water systems in a block of flats are in use.

Further advice for local health protection teams (HPTs), working with environmental health departments, in the investigation of household water systems following a case of LD is available in the following documents:

• UKHSA Legionnaires' disease: investigation of household water systems
• Scottish Health Technical Memorandum for Water safety (SHTM 04-01)

Travel-associated clusters and outbreaks of LD

Time period

The definition of a travel-associated cluster is where two or more cases have stayed overnight in or visited the same accommodation site within a two-year period.

The extended two-year period (as opposed to the six months for community cases) is used to account for the seasonal nature of popular travel destinations during the holiday season and consequently the seasonal occupancy of accommodation sites.

Management of clusters

Clusters associated with travel abroad should be managed in the same way as single-case investigations.

Full details should be collected from cases regarding their movements and accommodation during their time abroad. It is important to remember that the information recorded must be detailed enough to enable colleagues in the country of travel to identify the accommodation in which the case stayed. This information must be sent to the IHRNFP by the PHS Respiratory Bacterial Pathogen Team so that it can be provided to colleagues in the country of travel.

Location in Scotland

Where an accommodation site in Scotland is associated with a cluster or outbreak, the HPT local to the accommodation site should be informed and an investigation initiated.

In order to support the process of investigation, risk assessments and ongoing control measures of the accommodation site, the local HPTs can arrange for the completion of the Legionella accommodation site investigation report form by the relevant enforcing authority.

Completed forms should then be retained by the local HPT as a record of recommendations by the enforcing agency and resulting actions taken by the site operators that may be called upon for individual case reports or future investigations.

Please note that completion of this report is not mandatory and the following suggested timescales for completion and return of parts 1 and 2 of the report to the HPT are advisory only.

Investigation report form: part 1

This can be used to indicate whether a risk assessment and initial investigations have been carried out and control measures implemented and is typically completed within 2 weeks of the cluster being identified.

Investigation report form: part 2

This can be used to indicate whether control measures were satisfactory, remedial actions undertaken and the result of any sampling and is typically completed within 6 weeks of the cluster being identified.

Access the UKHSA Legionella accommodation site investigation report form, parts 1 and 2.

Further guidance

There is further guidance in the environmental investigations and sampling section on completing and retaining each part of the Legionella Accommodation Site Investigation Report.

Communications

Advice and guidance on communication can be found in the management of public health incidents guidance.

Any incident that meets the World Health Organization criteria for a serious public health impact must be notified under the International Health Regulations (IHR).

A major outbreak of legionellosis, particularly an outbreak considered to have international public health importance, would warrant notification under the International Health Regulations (2005) and, when requested, a WHO coordinated response, including support to the affected country and information to alert other countries of a potential health threat.

End of outbreak

The IMT decides on the end point of an outbreak, and ensures relevant partners are informed.

A summary of the incident should be submitted to the PHS Respiratory Bacterial Pathogen Team to ensure that all cases associated with the incident have been:

• reported
• linked to the cluster or outbreak
• logged in the national database

The information provided should be sufficient for the PHS Respiratory Bacterial Pathogen team to describe and draw conclusions about observed associations with potential sources of infection.

Roles and responsibilities of organisations involved in the investigation of Legionella incidents

NHS board health protection teams (HPTs)

Objectives

• Preventing people being put at risk from further exposure.
• Reducing complications, disabilities and mortality in those affected.
• Ensure appropriate clinical management of cases.
• Communicate with the public and agencies.

Legislative framework

Public Health etc. (Scotland) Act 2008

Section 2 of the Act places a duty on NHS boards to ensure provision is made within their area for the purposes of protecting public health.

Section 3 of the Act requires NHS boards to designate sufficient persons on behalf of the board for the purpose of protecting public health. This person is known by the term ‘Health Board Competent Person’.

Section 4 of the Act requires LAs to ensure provision is made within their area for the purposes of protecting public health. EHOs are the prime LA resource in health protection. EHOs also have responsibility for securing the abatement of public health nuisances through advice and enforcement and thereby reducing the risks from many environmental hazards, including Legionella.

Section 5 of the Act requires LAs to designate persons for the purpose of protecting public health. This person is known by the term ‘Local Authority Competent Person’. A LA Competent Person may also take or instruct any person to assist them with their investigations in whatever way they deem appropriate.

Section 6 of the Act places a duty on NHS boards and LAs to co-operate with each other in order to protect public health.

Under Part 3 of the Act, NHS boards are required to investigate public health incidents and carry out public health investigations.

Access the Public Health etc. (Scotland) Act 2008.

Actions

Through management of the IMT, the NHS board HPT will ensure that all key agencies clearly understand their respective roles, and carry out their investigative and management tasks promptly and effectively in co-operation with each other as required.

Local authorities (LA) Environmental Health

Objectives

• Protection of public health by seeking to prevent people being put at risk from further exposure.
• Investigation of potential sources of Legionella during an outbreak.
• Specialist Reporting Agency to the Procurator Fiscal Service with reporting responsibilities for investigations of crimes, including the failure to control the risk from Legionella in water systems.

Legislative framework

Public Health etc. (Scotland) Act 2008 and Health and Safety at Work etc. Act 1974 (HSWA 1974)

Both the HSE and LAs enforce the HSWA 1974 and the subordinate regulations and approved codes of practice in their respective areas of responsibility which are defined in the Health and Safety (Enforcing Authority) Regulations 1998.

Typically, LAs enforce health and safety at work legislation in hotels, care homes, leisure premises, warehouses, retail and office premises and catering premises.

On a day-to-day basis, officers in LAs carry out inspections and investigations under this legislation. Officers have statutory powers to ensure that where required, improvements are made in risk control, and where there is a risk of serious personal injury associated with a work activity that this activity is prohibited until appropriate controls are in place to safeguard those at risk of injury.

In terms of their proactive inspections, the HSE has published a list under the National Local Authority Enforcement Code of higher risk activities falling into specific LA enforced sectors. Under this code proactive inspection should only be used by LAs for activities which appear in the list of activities and within the sectors or types of organisations identified, or where there is intelligence showing that risks are not being effectively managed.

Access the:

• Public Health etc. (Scotland) Act 2008
• Health and Safety at Work etc. Act 1974 (HSWA 1974)

Actions

1. The LA pursues compliance with H&S legislation within those premises where they enforce the Health and Safety at Work etc. Act 1974 and related legislation. This compliance includes investigation of management systems and performance and potential sources of Legionella.
2. The LA will investigate potential sources of Legionella by examining site records and taking (or arranging to be taken) samples and specimens from risk systems within their area. Samples may include water samples (for both chemical and microbiological analysis), bio film swabbing and such other materials as may be considered necessary, for example composts and soils.
3. The LA provides advice to the duty holder on corrective action(s) to be taken to ensure that the risk system is brought under control where deficiencies are identified.
4. The LA has statutory powers to pursue enforcement action where necessary, in premises where they enforce the Health and Safety at Work etc. Act 1974.
5. The LA will work with the HSE where corrective action is considered necessary within premises where they enforce the Health and Safety at Work etc. Act 1974.
6. LA EHOs will, under the direction of the IMT, undertake interviews of cases in the community to clarify and gather further detailed information on movements and places visited.
7. LAs should consider putting a list of cooling towers on their website.

Public Health Scotland (PHS)

Objectives

• National surveillance of legionellosis to allow rapid identification of clusters and outbreaks.
• Preventing people being put at risk from further exposure by rapid investigation and control in any Legionella incident situation.
• Supporting outbreak investigation with specialist, timely and appropriate advice.
• Development of national guidance and best practice for use in Legionella incident situations.

Legislative framework

Public Health etc. (Scotland) Act 2008

Access the Public Health etc. (Scotland) Act 2008.

Actions

Public Health Scotland (PHS) works in partnership with others to protect the Scottish public from being exposed to hazards which damage their health and to limit any impact on health when such exposures cannot be avoided.

It seeks to achieve this aim by:

• promoting a consistent, efficient and effective approach in the delivery of health protection services by NHS and related agencies
• co-ordinating the efforts of public health agencies in Scotland in health protection especially when a rapid response is required to a major threat
• helping increase the public understanding of and attitudes to public health hazards and facilitating their level of involvement in the measures needed to protect them from these
• being the source in Scotland of expert advice and support to government, NHS, other organisations and the public on health protection issues
• helping develop a competent health protection workforce
• improving the knowledge base for health protection through research and development

The key health protection functions of PHS (for the purpose of this guidance) are:

• monitoring the hazards and exposures affecting the people of Scotland and the impact they have on their health
• co-ordinating national health protection activity
• facilitating the effective response to outbreaks and incidents
• supporting the development of good professional practice in health protection
• monitoring the quality and effectiveness of health protection services
• research and development into health protection priorities
• providing expert impartial advice on health protection
• promoting the development of a competent and confident workforce in health protection
• commissioning national reference laboratories.

For a localised incident affecting a single NHS board with no major disruption of services [note 1]

• maintain communication with and provide access to expert advice to the NHS board
• liaise when necessary with the Scottish Government and/or Food Standards Scotland
• if available, provide additional personnel to facilitate the management of the incident who will be managed for the relevant period by the NHS board
• work with the NHS board to assure the quality and effectiveness of the steps taken to manage the incident and in particular help ensure that there is a structured debrief
• health alerts arising from an incident
  • distribute information to relevant staff in the NHS and LAs, if appropriate
  • copy information to SG
  • respond to queries concerning the subject matter of the alert

For an incident affecting two or more NHS boards with no major disruption of services [note 1]

• agree with the NHS boards the appropriate management arrangements (such as a single IMT or two or more IMTs) – this may include as an option PHS assuming responsibility for leading the overall management of the incident on behalf of an NHS board
• on behalf of the parties to the joint arrangement, co-ordinate surveillance, investigation, risk assessment and management and risk communication
• operational management locally will remain the responsibility of NHS boards

For a Scotland or UK-wide incident with some but no major disruption of services (for example, a foodborne outbreak associated with a nationally distributed foodstuff) [note 1]

• lead the management of the incident in Scotland and establish appropriate arrangements on behalf of SGHSCD
• with regard to an incident affecting one or more of the countries in the UK, lead Scotland’s participation in UK-wide management arrangements – this may involve leading in certain circumstances the UK response
• co-ordinate surveillance, investigation, risk assessment and management and risk communication
• operational management locally will remain the responsibility of NHS boards

Notes

1. Taken from the Management of public health incidents: guidance on the roles and responsibilities of NHS-led incident management teams

Health & Safety Executive (HSE)

Objectives

The HSE is the independent regulator which acts in the public interest to reduce work-related death, serious injury and ill-health across many workplaces in the UK.

The mission is to ensure that risks in the workplace are properly controlled. HSE helps businesses understand how the laws to keep people safe at work affect them. Securing justice through investigation and enforcement where there are serious breaches of law and non-compliance is an important element of HSE’s powers.

Companies have a legal requirement to control the risks from Legionella. HSE publishes extensive guidance on the control measures which are necessary to minimise the risks and to comply with the legislation (ACoP L8).

HSE periodically carries out inspections of companies with registered cooling towers and evaporative condensers to ensure that controls for Legionella remain adequate and that workers and the public are protected.

Where there is evidence of serious non-compliance, in line with their Enforcement Policy Statement, HSE will use formal enforcement powers (Improvement or Prohibition Notices or recommendation of legal proceedings to the Crown Office and Procurator Fiscal Service (COPFS)).

Legislative framework

Health and Safety (Enforcing Authority) Regulations 1998 

These regulations allocate workplace activities to either HSE or LAs for enforcing health and safety legislation. HSE deals with health and safety in factories, farms, hospitals and schools, offshore gas and oil installations, the safety of the gas grid and the movement of dangerous goods and substances, nuclear installations and mines and many other aspects of the protection both of workers and the public throughout various industry sectors.

Access the Health and Safety (Enforcing Authority) Regulations 1998.

Health and Safety at Work etc. Act 1974 (HSWA 1974)

Section 2 requires employers to ensure so far as is reasonably practicable the health, safety and welfare at work of all his employees.

Section 3 requires employers to conduct their undertaking in such a way as to ensure, so far as is reasonably practicable, that persons not in their employment who may be affected thereby are not thereby exposed to risks to their health or safety. This is the main duty relevant to outbreaks affecting the public offsite.

Access the Health and Safety at Work etc. Act 1974 (HSWA 1974).

Approved Code of Practice (ACoP L8)

The Approved Code of Practice (ACoP L8) is approved by virtue of Section 16(4) of the HSWA 1974. It has a special legal status and an employer has to follow the ACoP L8 or show that they have complied with the law in some other way. The ACoP L8 applies to the risk from Legionella bacteria (the causative agent of legionellosis including Legionnaires’ disease) in circumstances where the Health and Safety at Work etc. Act 1974 applies.

ACoP L8 gives practical advice on the requirements of the Health and Safety at Work etc. Act 1974 (HSWA 1974) and, the Control of Substances Hazardous to Health Regulations 2002 (COSHH) (as amended), (2005) concerning the risk from exposure to Legionella bacteria. In particular, it gives guidance on sections 2, 3, 4 and 6 (as amended by the Consumer Protection Act 1987) of HSWA and regulations 6, 7, 8, 9 and 12 of COSHH 05. The Code also gives guidance on compliance with the relevant parts of the Management of Health and Safety at Work Regulations 1999 (MHSWR).

Access the Approved Code of Practice (ACoP L8).

Public Health etc. (Scotland) Act 2008

HSE does not enforce the Public Health Act. HSE does not sample water systems. During an outbreak LAs are empowered to take samples in HSE enforced premises under the Public Health Act.

Access the Public Health etc. (Scotland) Act 2008.

Actions

1. Preventing people being put at risk from further exposure by taking appropriate action in HSE enforced workplaces to ensure that the risks from Legionella are prevented or controlled in the outbreak zone, and seeking to ensure sustained compliance with H&S legislation.
2. Stopping growth of the organism and reducing the risk from Legionella growth in water systems by providing advice on corrective action to control Legionella in affected premises, and pursuing enforcement action where necessary; ensuring compliance with ACoP L8.
3. In the event of an outbreak HSE will contribute to IMT decisions on the extent of the outbreak zone, the priority order of potential sources of Legionella, and provide specialist advice as required.
4. HSE along with the LA as co-partners will seek to investigate all relevant priority premises in the outbreak zone. HSE will make a decision as to which HSE enforced premises to visit, based on a number of factors including registered cooling towers, local knowledge and advice of the IMT.
5. HSE will seek to ensure that the water systems do not present a risk to workers or the public and that the potential for further cases of infection are minimised.
6. HSE will seek to ensure compliance with legislation and that adequate arrangements are put into place for the on-going and sustained control of Legionella risks. HSE will often specify the necessary corrective actions to decontaminate water systems and to achieve adequate control, using formal enforcement notices as necessary.
7. HSE will advise employers if the towers need to be shut down as a precautionary measure, voluntarily. HSE is unable to prohibit the use of cooling towers unless sufficient evidence of an out of control system is available to sustain a Prohibition Notice. In the early stages of outbreak investigations such evidence is often not available. Employers have a legal right to appeal any Notices to an Employment Tribunal, so HSE must be sure that there is sufficient evidence to substantiate their actions.
8. HSE will investigate to secure justice. HSE (where it is the enforcing authority for the workplace) will investigate the outbreak in partnership with COPFS and the Police in line with the Work Related Deaths Protocol for Scotland, where deaths have already occurred or are likely.

Clinical microbiology laboratories

Objectives

• Identifying the causative organism in human cases of legionellosis.

Legislative framework

Clinical microbiologists perform a diagnostic function as determined by their commissioning body.

Additional work related to an incident will be as directed by the IMT.

Actions

NHS diagnostic laboratory microbiologists will:

• provide laboratory confirmation of clinically suspected cases
• notify detection of Legionella species in diagnostic samples to clinicians and the local HPT
• report cases and suspected cases to the local HPT
• refer appropriate samples and all isolates to the reference laboratory and liaise with reference laboratory staff
• provide advice on investigation and management of suspected and confirmed cases as required;
• communicate with clinical colleagues as required
• attend IMT meetings

Reference laboratory microbiologists will:

• ensure provision of appropriate reference laboratory tests
• report results to the local diagnostic laboratory microbiologists
• liaise with diagnostic laboratory microbiologists, PHS and local HPTs as appropriate
• attend IMT meetings

Public analyst laboratories

Objectives

• Identifying the causative organism in environmental samples taken in association with cases of legionellosis.

Legislative framework

Public Analyst microbiologists perform a diagnostic function as determined by their commissioning body.

Additional work related to an incident will be as directed by the IMT.

Actions

• Provide sampling and examination advice to LA EHOs and participate in sampling as appropriate.
• Examine water, biofilm, sludge, soils and other environmental materials using suitable microbiology methods to identify the causative organism in human cases.
• Test water and other environmental samples to ensure that chemical and other parameters are compliant with regulatory requirements such as HSE document L8 to ensure putative Legionella sources are in control.
• Link with the SHLMPRL to assist in the characterisation and identification of the causative organism in human cases.
• Assist the police and prosecuting authorities in taking and testing water and other environmental samples from the homes of persons suspected to have been infected with Legionella, where appropriate.
• Attend IMT meetings to provide scientific advice and support.

Scottish Government

Objectives

• To support the response and recovery efforts.
• Where there is a significant incident, provide strategic direction for Scotland.

Actions

The CMO and Public Health Directorate, Health Protection Team is the main point of contact for public health incidents. Where this risk is considered low then the Health Protection Team will monitor the situation to ensure that all necessary measures are taken by statutory agencies and that information is effectively communicated to the public and between agencies. This may involve participation as an observer in IMT.

When the scale or complexity of an incident is such that it would benefit from central government coordination or support, the Scottish Government will activate its emergency response arrangements through the Scottish Government Resilience Room (SGoRR). The role of SGoRR will vary according to the nature, scale and impact of the incident.

Scottish Government has prepared guidance on resilience:

• Prepare Scotland
• management of public health incidents (together with the Scottish Health Protection Network (SHPN))

Crown Office and Procurator Fiscal Service (COPFS)

Objectives

The Lord Advocate through COPFS, is responsible for investigating all sudden, suspicious or unexplained deaths and is the sole prosecuting body in Scotland.

Legislative framework

Corporate Manslaughter and Homicide Act 2007

An organisation commits corporate homicide if the way in which its activities are managed or organised causes the death of a person and amounts to a gross breach of a relevant duty of care owed by that organisation to the victim. The way its activities are managed or organised by its senior managers is a substantial element.

The Work-Related Deaths Protocol establishes the partnership working required to investigate where there is suspicion that a serious offence (other than a health and safety offence) may have caused the death. Police Scotland will assume primacy for the investigation, directed by COPFS and in partnership with HSE or other enforcing authority.

Access the Corporate Manslaughter and Homicide Act 2007.

Actions

COPFS will direct the Police Scotland investigation into the deaths to establish if there is evidence of serious criminal offences and will work in partnership with HSE or other enforcing authorities.

COPFS will work with the IMT to ensure clear links and demarcations between the police and IMT investigations.

COPFS will work with the IMT to balance risk of withholding IMT investigation findings and the effect on public health, with potential prejudice to the criminal investigation from releasing investigation findings.

It is a duty of the forensic pathologist, working under the direction of the Procurator Fiscal, to ensure that samples delivered from relevant laboratories are delivered in a manner which preserves the chain of evidence.

Employers and industry

Legislative framework

Health and Safety at Work etc. Act 1974 (HSWA 1974) and Approved Code of Practice (ACoP L8)

Access the:

• Health and Safety at Work etc. Act 1974 (HSWA 1974)
• Approved Code of Practice (ACoP L8)

Role

Employers should ensure compliance with the relevant legislation in order to control growth of Legionella within their water systems. It is not illegal for employers to have Legionella in water systems as the organism cannot be fully eliminated, but the risk must be controlled.

The employer is innocent until proven guilty in a court and the IMT and regulators must avoid speculation about the source which could have significant adverse repercussions for any potential future legal proceedings as well as an employer’s reputation. Identification of a source does not necessarily imply criminal act but is necessary to protect the public.

Note

Employers are likely to take legal advice from the initial investigation stage onwards, and regulators and/or the IMT may face challenge about powers, sampling techniques, laboratory tests etc.

Employers will normally voluntarily shut down towers and water systems if requested to by HSE or LA, as a precautionary measure to enable further detailed analysis and investigation. Should HSE or the LA use formal enforcement powers, the employer is entitled to appeal to a Tribunal.

Employers should provide sufficient information about potential sources to identify cases and further protect health.

Guidance development method

Guidance development process

Method

PHS developed this guidance in line with the approach for reviewing and updating existing guidance documents.

This aligns with the Scottish Health Protection Network (SHPN) approach.

View the PHS method for guidance development.

Guidance Development Group

A multidisciplinary Guidance Development Group (GDG) was convened to produce this guidance.

The GDG had representation from:

• ARHAI Scotland
• NHS board microbiology services
• NHS health protection teams (HPTs)
• Public Health Scotland (PHS)
• Scottish Health Protection Network (SHPN)
• Scottish Microbiology Reference Laboratory (SMiRL)
• Scottish Microbiology and Virology Network (SMVN)
• Environmental Public Health (EPH)
• Health and Safety Executive (HSE)
• Environmental Health Departments at South Lanarkshire Council, City of Edinburgh Council and East Renfrewshire Council
• Scottish Government
• NHS Orkney and NHS Forth Valley.

Each GDG member returned a conflict-of-interest form. No competing interests were declared by GDG members.

Evidence base

This guidance update focused on streamlining the existing:

• Health Protection Scotland and Scottish Health Protection Network 2018 guidance
• UK Health Security Agency 2022 guidance for the management of Legionnaires' disease

It refers to partner agencies for more detailed advice on their respective areas of expertise.

The GDG critically appraised the UKHSA guidance using the AGREE-II instrument to assess the methodological rigor, clarity, and applicability of the UKHSA guidance in Scotland, identifying strengths and areas for improvement. The findings informed the development process, ensuring that the new guidance aligns with best practices and enhances its relevance for health protection.

The GDG critically appraised the UKHSA guidance using the AGREE-II instrument to assess the methodological rigor, clarity, and applicability of the UKHSA guidance in Scotland, identifying strengths and areas for improvement. The findings informed the development process, ensuring that the new guidance aligns with best practices and enhances its relevance for health protection.

It was agreed that a review of the full evidence base underpinning the UKHSA 2022 guidance was not required.

However, the GDG suggested that a focused review of the scientific evidence supporting various recommendations was required to inform decision-making.

Evidence review

A review of the evidence on the following key questions were agreed by the GDG in order to focus the literature search.

• What are the possible sources of infection and the specific characteristics related to Legionnaires' disease? 
• How many kilometres should be considered at the investigation of possible clusters in community-acquired cases of LD?
• How many days (duration at risk of exposure) before symptoms onset should be considered at the investigation of an incident, cluster or outbreak of LD and possible sources of infection? 

Search strategy

Healthcare scientists from the PHS Respiratory Team designed the systematic literature search based on key terms relating to the key questions.

Read our full evidence summary document.

Review of literature

Each title and abstract, as well as the full text, were screened by a single reviewer. However, the extraction process was conducted by a team of two people.

This was undertaken using Sciwheel, and extraction data was added to a table.

Systematic critical appraisal of all included papers was limited, due to the resources available. However, principles of critical appraisal were considered in the evidence review.

Evidence

Evidence identified

A narrative summary of the evidence review was produced and shared with the GDG.

Evidence to recommendation

The GDG considered the UKHSA guidance recommendations in the Scottish context and highlighted areas where further discussion and agreement where required, taking into account the evidence reviewed. The group developed recommendations for the specific Scottish context and pathways.  

Expert opinion on particular areas of the guidance was also sought during GDG meetings or via email. Agreement on the final recommendations was achieved through consensus.

Based on the considered judgement process carried out, all recommendations are considered to be good practice recommendations, as they are primarily based on expert opinion.

Consultation

Consultation with stakeholders took place in February and March 2025 and was open for four weeks. The consultation feedback was reviewed by the GDG.

An Equality Impact Assessment (EQIA) was carried out while the GDG was formulating recommendations and the document recording that exercise was circulated among the GDG members for further comments and refinement.

Both the guidance and EQIA were updated accordingly.

Approval and review

PHS and the SHPN Guidance Group have approved this guidance in line with current governance process supporting the development of guidance for health protection in Scotland.

In line with the SHPN method, the guidance will be reviewed at least every three years from its publication date.

Equality impact assessment (EQIA)

The equality impact assessment (EQIA) was written alongside the guidance development process and was reviewed by the GDG, as the group considered the feedback received in the consultation phase.

This EQIA was conducted to evaluate the differential impact of the guidance recommendations on population subgroups with protected characteristics.

Download the EQIA

Abbreviations