• Assessing the risks
• Developing a written scheme for preventing and controlling the risks
• Implementing and auditing the scheme.

• Identify and assess the risk of exposure to Legionella bacteria from work activities and water systems on a premises i.e. a workplace, healthcare facility or leisure facility
• Establish any necessary preventive and control measures.

• The employer or self-employed person in order to assess the risk to employees, themselves or to others
• The person in control of a premises or systems where the risk may be present (e.g. the CEO of the hospital)
• The person in control of a premises used for overnight accommodation such as hotels, holiday apartments, campsites and cruise ships where the risk may be present from water systems in the building/site.

• The potential for Legionella seeding and growth
• The potential for aerosol generation and exposure
• The presence of susceptible persons
• The adequacy of existing site management arrangements and records
• The efficacy of existing preventive and control measures.

• To identify and evaluate potential sources of risk
• To identify means of preventing and controlling exposure and if prevention is not reasonably feasible, the particular means by which the risk from exposure to Legionella bacteria can be controlled, and To provide direction on prioritising actions for prevention and control.

4.3 Process of risk assessment

When undertaking a risk assessment, the individual nature of each site must be taken into account. In complex systems or premises, a site survey of all the water systems should be carried out and should include an asset register of all associated plant, pumps, strainers and other relevant items. This should include an up-to-date diagram/drawing showing the layout of the plant or system including parts temporarily out of use. A schematic diagram would be sufficient. It should then be decided which parts of the water system, for example which specific equipment and services, may pose a risk to those at work or to other people.

• The following systems present a potential risk of exposure to Legionella bacteria:
• Water systems incorporating a cooling tower
• Water systems incorporating an evaporative condenser
• Hot and cold water systems
• Spa pools
• Humidifiers
• Dental chair waterlines
• Natural thermal springs and their distribution systems

Other plants and systems containing water which is likely to exceed 20oC and which may release a spray or aerosol (i.e. a spray of droplets and/or droplet nuclei) during operation or when being maintained.

A water system includes all plant/equipment and components associated with that system e.g. all associated pipe work, pumps, feed tanks, valves, showers, heat exchangers, quench tanks, chillers, etc. It is important that the system is considered as a whole and not for example the cooling tower in isolation. Dead legs and parts of the system used intermittently also need to be included as they can create particular problems with microbial growth and go unnoticed. Other systems e.g. humidifiers and air washers, spa pools and baths, car/bus washes, wet scrubbers, industrial water systems, fountains and water features also need to be considered.

The following list contains some of the factors which should be considered when undertaking a risk assessment:

• The source of the system supply water, e.g. whether from the mains supply or not
• Possible sources of contamination of the supply water within the premises before it reaches the cold water storage cistern, calorifier, cooling tower or any other system using water that may present a risk of exposure to Legionella bacteria
• The design, location and condition of equipment for example the position of air intakes for buildings in relation to the location of cooling tower exhausts
• Conditions suitable for multiplication of the microorganisms e.g. stagnant water, suitable temperature (20oC-45oC), and a source of nutrients e.g. sludge, scale, rust, algae and other organic matter
• A means of creating and disseminating inhalable droplets e.g. aerosols generated by cooling towers, showers or spa pools
• Normal equipment operating conditions and any unusual but foreseeable conditions e.g. equipment breakdown
• The presence of vulnerable individuals e.g. immunocompromised individuals who may be exposed to infection

The extent of exposure - the number of people who may be exposed and the length, duration and frequency of exposure.
Not all systems will require elaborate risk assessment and control measures. A simple risk assessment may show that the risks are low e.g. small domestic-type premises where temperature and turnovers are high and where instantaneous water heaters are used. In such cases no further action may be required other than to review the risk assessment on a regular basis.

Where a risk is identified, the significant findings of the assessment should be recorded, together with the name of the person and organisation who carried out the assessment. It will also be necessary to record sufficient details of the assessment to be able to show that it has been done. It should be linked to other relevant health and safety records

Failure to undertake a risk assessment or possession of an inadequate risk assessment may lead to prosecution, especially if a system or premises is implicated in a Legionnaires disease outbreak.

4.4 Preventing or controlling the risk

The risk rating for exposure to Legionella can be categorised as follows:

• VERY HIGH - where it is certain or near certain that exposure will occur
• HIGH - where exposure will often occur
• MEDIUM - where exposure will sometimes occur
• LOW - where exposure will seldom occur

INSIGNIFICANT OR NOT FORESEEABLE.

Where an assessment determines that there is a potential risk of exposure to Legionella bacteria, the use of water systems, parts of water systems or systems of work that lead to exposure have to be avoided as far as is reasonably practicable. Where it is not practicable to do so then control measures should be adopted to minimise exposure.

Guided by the risk ratings outlined above, actions for the prevention or control of exposure to Legionella should be prioritised by adopting:

• Urgent corrective actions to prevent or control exposure from water systems or activities categorised as VERY HIGH or HIGH RISK
• Planned corrective actions to meet L8 guidance or equivalent for medium and low risk

4.5 Implementing a control scheme

The implementation of a control scheme should be regularly and frequently monitored and decisions should be made on the frequency and manner of the monitoring procedures (see Section 4.15). The effectiveness of the programme should also be monitored including the impact of short-term or interim measures. Regular review and updating of risk ratings is crucial to the success of the control scheme and the implementation programme should be updated to take account of any changes in priorities and timescales.

All persons involved in the operational procedures should be properly supervised. Staff roles, responsibilities and lines of communication should be properly defined, clearly documented in writing and understood by all involved.

Communications and management procedures are particularly important where several people are responsible for different aspects of the operational procedures. Lines of communication should be clear, unambiguous and audited regularly to ensure that they are effective.
The above also applies to the outside companies and consultants who may be responsible for certain parts of the treatment regime. The employment of contractors or consultants does not absolve the duty of the holder of responsibility for ensuring that control measures are in place to the highest standard to prevent the proliferation of Legionella bacteria.

Arrangements should be made to ensure appropriate staffing levels are maintained during all hours that water systems are in operation. Appropriate arrangements should be made to ensure that the responsible person or an authorised deputy can be contacted at all times. Details of the contact arrangements for emergency call out personnel should be clearly displayed at access points to all automatically or remotely controlled water systems.

A written scheme detailing measures to prevent or control risks should be implemented and properly managed, including:

An up-to-date schematic of the plant, building or system, including parts temporarily out of use

A description of correct and safe operation

Precautions to be taken and checks to be conducted to ensure the efficacy of the scheme and frequency of such checks

Remedial action to be taken if the scheme is shown not to be effective.

Based on the above scheme, a programme should be developed for implementation of control measures taking account of risk ratings, site requirements, resources and short-, medium- and long-term options for preventing and reducing risks as far as is reasonably practicable. This will require communication between the risk assessor, service provider and the responsible person.

The risk from exposure will normally be controlled by measures, which do not allow the proliferation of Legionella bacteria in the system and reduce exposure to water droplets and aerosol. These include engineering controls, cleaning protocols and other control strategies such as:

Controlling the release of water sprays

Avoidance of water temperatures and conditions which favour the proliferation of Legionella bacteria and other microorganisms i.e. avoiding water temperatures between 20oC and 50oC. Water temperature is a particularly important factor in controlling the risks and should be either below 20oC or above 50oC.

• Avoidance of water stagnation that can encourage the growth of biofilm (slimes that form on surfaces in contact with water) which can harbour Legionella bacteria and provide local conditions that encourage growth
• Avoidance of the use of materials which harbour bacteria and other micro-organisms or provide nutrients for microbial growth e.g. rubber washers and hoses
• Maintenance of the cleanliness of the system and the water in it in order to avoid the build up of sediments which may harbour bacteria (and also provide a nutrient source for them)
• Use of water treatment regimes/techniques where it is appropriate and safe to do so
• Action to ensure the correct and safe operation and maintenance of the water system.

Decisions should be made about the maintenance procedures and intervals and where relevant on equipment used for carrying out the control measures. Legionella bacteria may be present in low numbers in many water systems but careful control will prevent them from multiplying. The scheme should give details on how to use and carry out the various control measures and water treatment regimes including:

The physical treatment programme e.g. the use of temperature control for hot and cold water systems (see Section 4.15.3b)

The chemical treatment programme including a description of the manufacturer's data on effectiveness, the concentrations and the contact time required

Health and safety information for storage, handling, use and disposal of chemicals

System control parameters (together with allowable tolerables); physical, chemical and biological parameters, together with measurement methods and sampling locations, test frequencies and procedures for maintaining consistency

Remedial measures to be taken in case the control limits are exceeded including lines of communication

• Cleaning and disinfection procedures.
• There should also be a description of the correct operation of the water system plant including:
• Commissioning and recommissioning procedures
• Shutdown procedures
• Checks of warning systems and diagnostic systems in case of system malfunctions
• Maintenance requirements and frequencies
• Operating cycles - including when the system plant is in use or idle.

4.6 Review of control measures - monitoring and routine inspection

If preventive measures are to be effective, the condition and performance of the system will need to be monitored. This should be the responsibility of the responsible person or where appropriate an external contractor or an independent third party should be involved.

This will involve:

• Checking the performance of the system and its component parts
• Inspecting the accessible parts of the system for damage and signs of contamination
• Monitoring to ensure that the treatment regime continues to control to the required standard.

The operating characteristics of the water distribution network e.g. pumps should be monitored at least once weekly. The results of monitoring and testing should be interpreted by a suitably experienced and competent person and any remedial measures where necessary should be carried out promptly.

Testing of water quality is an essential part of the treatment regime, particularly in cooling towers. A service provider e.g. a water treatment company or consultant may undertake it provided that they are trained to do so and properly supervised. The type of tests required will depend on the nature of the system.

The routine monitoring of the general aerobic heterotrophic bacterial count (total viable count) is also a very important indicator of whether microbiological control is being achieved. This should be routinely undertaken for cooling towers (see Section 4.15.3 and Chapter 5, Section 5.2.2) and spa pools (see Chapter 7, Section 7.5.9). In relation to hot and cold water systems, this should be undertaken periodically. Depending on the size of the water system, samples should be taken from the following points in the system: the calorifier, water tank, pipes midway along the system and from the furthest point from the water tank/boiler. Sampling twice a year and testing for the presence of Legionella bacteria may also be appropriate as an indication that adequate control is being achieved.

In order to ensure effective implementation of the control programme, a compliance checklist should be compiled which includes:

• Responsibilities allocated
• Risk assessments up-to-date
• Written control scheme implemented
• Written control scheme working
• Satisfactory closure of non-compliances
• Emergency action procedures
• Process of management review
• Records complete and up-to-date.

4.7 Frequency of risk assessment

Once the risk assessment is completed and documented, it should be reviewed regularly i.e. at least annually. If there are significant alterations to operational procedures in the institution or significant changes to the water distribution system then the risk assessment should be reviewed and updated. There should be a written record of this review. In addition, it will need to be repeated more frequently in situations where the original assessment is considered to be no longer valid. An indication of when to review the assessment and what needs to be reviewed should be recorded. This may result from:

• Changes in the water system or its use
• Changes in the use of the building in which the water system is installed
• The availability of new information about risk and control measures
• The results of checks indicating that control measures are no longer effective
• A case of Legionnaires disease/legionellosis associated with the system.

4.8 Written risk assessment

A written risk assessment should include:

• The scope of the assessment
• A description of the site and water systems with details of design, operation and maintenance
• Details of site arrangements for managing and recording control of Legionella risks
• Assessment of risk for each system and activity

Recommendations for preventing (elimination of source of bacteria, aerosols or exposure) or controlling (control bacteria re-growth, aerosol release and exposure) the risks including monitoring, remedial actions, etc.

Control measures may include:

• A regular regime of water treatment, cleaning and disinfection, monitoring and maintenance and/or
• One-off actions such as setting up management and record/documentation systems, plant or equipment improvements, modifications, refurbishments and replacements.

4.9 Record keeping

The responsible person(s) appointed must ensure that appropriate up-to-date records relating to the control scheme are kept. These records should include the following details:

Names and positions of person(s) responsible for carrying out the various tasks under the written scheme i.e. responsible for risk assessment, managing and implementation of the control scheme

Plans and schematic drawings of the systems

Details showing the current state of operation of the system e.g. when the system or plant is in use and if not in use whether it was drained down or not

The significant findings of the risk assessment

The written scheme of actions and control measures required and details of their implementation

The results of any monitoring, inspection, test or check carried out, and the dates

A log detailing visits by contractors, consultants, and other personnel. The remedial work required and carried out and the date of completion

The signature of the person carrying out the work or other form of authentication where appropriate i.e. contract specification

• Copies of contractor's method statements
• Cleaning and disinfection procedures and associated reports and certificates
• Results of the chemical and microbiological analysis of the water
• Information on other hazards e.g. treatment chemicals
• Personnel training records
• Review meeting notes and actions
• Product information and chemical/biocide safety data sheets.

Records kept in accordance with the above should be retained throughout the period for which they remain current. All test and inspection records must be kept for five years from the date of the test or inspection. All records should be signed by those persons performing the various tasks assigned to them.

4.10 Managing the risk: responsibilities, training and competence

It is imperative that a competent person with the relevant skills, knowledge and experience carries out the risk assessment. Organisations and individuals carrying out risk assessments should ideally be members of a recognised professional body or association e.g. the Legionella Control Association in the UK or equivalent. If this level of expertise is not available within the organisation, then it should be sourced externally. Sections 8 and 19 of the 2005 Safety, Health and Welfare at Work Act outline in detail the legal duties of the employer in this regard and the legal requirements in relation to hazard identification and risk assessmen).

The person on whom the corporate responsibility for the premises/systems lies should have access to such expertise. In order to prevent any conflicts of interest, it is recommended that ideally, those appointed to carry out the risk assessment are independent of those appointed to implement the control measures and remedial actions, including water treatment and cleaning and disinfection. It is the duty of the employer to ensure that those undertaking the risk assessment are competent and suitably trained and have the necessary equipment to undertake the risk assessment in a safe and adequate manner.

If the risk assessment identifies that there is a potential risk and it is practicable to prevent exposure or to control the risk from exposure, the person on whom the corporate/statutory obligation falls e.g. CEO, employer, etc. should appoint a responsible person to take managerial responsibility and provide supervision for the implementation of the precautions and for ensuring that:

• Persons involved in the implementation of the control scheme are trained and competent
• Responsibilities and lines of communication are properly established and clearly defined
• Management arrangements and communication procedures are reviewed periodically.

The responsible person should be a manager or director, or have similar status with sufficient authority, degree of competence and knowledge of the installation and resources to ensure control measures and systems operations are carried out in a timely, safe and effective manner. The competence required of the responsible person will depend upon the risks they have to manage, i.e. the nature, size, age, use and complexity of the water systems for which they are responsible. For locations with medium- to high-risk water systems the responsible person should have attended specific training courses on the management and control of risks of exposure to Legionella bacteria given by a qualified training provider. They should also attend regular refresher courses and attendance at all courses should be recorded. They should have a clear understanding of their duties and the overall health and safety management structure and policy of the organisation. This person will have day-to-day responsibility for the prevention and control of Legionella bacteria in the organisation.

Persons who carry out risk assessments and who devise and implement precautionary measures should have such ability, experience, information, training and resources to carry out their tasks competently and safely. In particular they should know:

• Potential sources of Legionella bacteria and the risks they present
• Measures to be adopted, including precautions to be taken for the protection of people concerned and their significance
• Measures to be taken to ensure that controls remain effective and their significance.

When the person(s) do not possess the above expertise, it may be necessary to enlist assistance and support from outside the organisation. In such circumstances, the responsible person should take all reasonable steps to ensure the competence of such organisations and the individuals undertaking the work.

4.11 Audit

A competent person should audit the implementation and performance of the risk management programme periodically (at least every two years). This person should be completely independent of the service providers responsible for the implementation of the risk control regime and should have no interest in the provision of such services.

4.12 Responsibilities of suppliers and service providers

Outbreaks of Legionnaires disease have been associated with faulty installation of equipment53 and inadequate application of water treatment and risk control regimes. As outlined in Chapter 3 on legislation, suppliers and service providers have duties and responsibilities under occupational health and safety legislation and must ensure that:

• Equipment is designed and constructed to be safe and without risks to health when used at work
• Adequate information is provided to the user about risk and measures necessary to ensure that water systems will be safe and without risk to health when used. This should be updated in the light of any new information about significant health and safety risks that becomes available.
• Products and services are fit for purpose and that any limitations are clearly defined and made known to responsible persons
• Staff have the necessary ability, experience, instruction, training and resources to carry out tasks competently and safely
• A written risk assessment is undertaken and a plan of work/method statement for their work activities is prepared so that such activities are planned, organised and controlled.

4.13 Reducing Legionella risks in new and refurbished buildings

Water systems should be designed, installed and commissioned to ensure risks from Legionella bacteria are eliminated wherever possible, or reduced as far as is reasonably practicable. Designs should also ensure that adequate provisions are made to facilitate safe system operation and maintenance since a poorly designed system can be both difficult and expensive to operate and maintain.

The 'designing out' of features that will increase the potential for seeding, growth and aerosolisation of Legionella should be regarded as an integral component of an effective risk control strategy, e.g. cold and hot water systems should be designed to preserve supply water quality, prevent microbial growth, eliminate or reduce formation of aerosols, minimise corrosion and maintain internal surfaces in a clean condition. This can be achieved by, for example:

• Utilising unvented direct mains supplied hot water systems
• Avoiding water storage tanks supplying calorifiers
• Using point of use water heaters rather than centralised hot water systems
• Designing hot water storage vessels, direct fired hot water service boilers and calorifiers to ensure adequate control of water temperatures in storage and distribution, and with sufficient heating capacity to enable periodic pasteurisation of their contents
• Using cold water storage tanks that optimise the maintenance of potable water quality with a storage capacity of no more than 24 hours average water demand
• Minimising the distance between the source of the water supply and point of use. Zoning should be used where appropriate in more complex systems
• Designing distribution systems to ensure regular throughput of water by eliminating 'dead legs' and long pipework runs
• Hot and cold water distribution pipework should be installed to minimise the transfer of heat between both. Appropriate insulation of pipes is essential.
• Ensuring that fittings, materials and components are corrosion-resistant and are constructed of approved materials which do not release nutrients into the water to support microbiological growth
• Avoiding use of equipment such as spray taps which generate aerosols where suitable alternatives are available. Where it is essential (e.g. showers) then equipment should be selected to facilitate routine cleaning and disinfection
• Sources of aerosols or droplets should be sited away from direct intake sites such as air vents and open windows.

It is important that the total requirements for water supply and quality are assessed in the planning stages, and water systems appropriate to areas of accommodation are allocated. Where a building project is completed and commissioned in phases or it is anticipated that areas of the building are likely to have different levels of occupancy and usage then careful consideration should be given to zoning of the water services to enable floors and areas of the building to be isolated and operated independently.

Installation and commissioning also require careful planning and execution to ensure designs are properly implemented and the necessary pre-commissioning cleaning and disinfection are carried out in accordance with industry standards and completed in time for hand-over. Long delays between completing the system disinfection and operating the water system will result in a deterioration in water quality and should be avoided.

Only competent service providers should be appointed to design, install or modify water systems. For those installations or modifications which could significantly affect the risk of legionellosis from the system, the appointed service provider should submit the following to the appropriate responsible person:

• A detailed description of the proposed new system, including a schematic drawing showing the layout of all component parts and identifying changes to existing systems
• Confirmation that its design and construction complies with relevant legislation, guidance and standards
• A risk assessment which considers the risk of legionellosis arising during the installation, including from any changes to existing systems, and identifies the precautions required to mitigate against these risks.

This information should be submitted to the responsible person at a reasonable period in advance of commencement of the work. The work should not proceed until it has been approved by the responsible person or by a nominated deputy in their absence.
On receipt of the information specified in the section above, the responsible person, or their nominated deputy should review the submission within 20 working days to consider whether:

• The system design allows it to be subsequently adequately maintained
• The assessment of risk is suitable and sufficient, with precautions adequate to minimise the risks, for example, from creation of dead legs and blind ends, from possible contamination of the system, etc.
• Arrangements are in place to monitor the work and ensure adequate commissioning of the system
• Necessary contingency measures will be put in place to minimise potential disruption to business operations and welfare facilities, for example, by provision of alternative water supplies, communicating changes, etc.
• The site can be cleared of other work and properly prepared
• Adequate and appropriate records will be provided, including sufficiently detailed 'as-fitted' plan or schematic drawings, operations and maintenance manuals, etc.

Once satisfied that all necessary safety arrangements are in place, the responsible person should approve the work and notify the designer/installer.

Larger and more complex projects will often benefit from a multidisciplinary approach involving, for example, designers, architects, manufacturers, installers, risk assessors, water quality specialists, microbiologists, operatives and users.

4.14 Materials for construction of water distribution networks

As Legionella bacteria are usually associated with bacterial biofilms and biofouling in water systems, consideration should be given to the materials used in the construction of water distribution networks. Previous studies with a range of materials commonly used in the construction of water systems showed that some materials were very good at limiting colonisation and biofilm formation by a wide range of bacterial species, whereas other materials were very poor. Copper was the best at limiting colonisation and biofilm formation, followed by polybutylene and stainless steel, whereas biofilm formed more readily on polyethylene, chlorinated polyvinyl chloride (PVCc), unplasticised polyvinyl chloride (PVCu), steel and ethylene-propylene.54;55 Distributing hot and cold water using copper pipes may significantly improve the microbial quality of water in water distribution networks as copper has been shown to possess significant antimicrobial advantages over water pipework of other composition.

4.15 Technical guidelines for the control and prevention of Legionella in water systems

An effective water treatment regime is essential for Legionella control. In addition to controlling legionellae, water treatment must also address the control of general microbial activity, biofilm development, corrosion, scale deposition and the retention of particulate solids. A cooling tower for example, with an inadequate or poorly controlled water treatment programme will be more vulnerable to contamination with legionellae and, therefore, present a much higher risk of exposure. Similarly, a distribution system which is fed with water containing sediment, minerals, organic matter and biofilm seed will always present a high risk. Removal or control of these elements does much to reduce the risk and also reduces the requirements for residual disinfection.

In assessing the adequacy of water treatment, cleaning, disinfection and maintenance regimes particular attention should be paid to:

• Biocide type, dosage rate and frequency, and half-life
• Efficacy of corrosion/scale control
• Operation and calibration of dosing/control equipment
• Maintenance of pre-treatment and ancillary plant
• Adequacy of cleaning and disinfection.

4.15.1 Flushing

The risk of nosocomial legionellosis attributed to the colonisation of hot and cold water systems by Legionella bacteria is well established. In a study of ten hospitals that were colonised by Legionella and ten that were not colonised, Legionnaires disease was found significantly more often in colonised than non-colonised hospitals (p = 0.054).56 In a study of 20 Spanish hospitals, nosocomial Legionnaires disease was found in 64.7% of the hospitals with water cultures positive for Legionella, whereas no nosocomial cases were found in hospitals with Legionella-negative water cultures.

Exner et al in their review of the literature on nosocomial infections cites a German study which investigated hospitals and residential units and other buildings that could be affected by the colonisation of the water system with Legionella bacteria.58 In the study, local colonisation of the water system was defined as colonisation of isolated parts of the plumbing system (taps or showerheads). Systemic colonisation was defined as colonisation of the whole system, including the central parts of the water supply. In the case of local colonisation it was possible to flush out Legionella bacteria from the distal water sites e.g. taps, showers. However, with systemic colonisation even intensive system flushing had no effect on the reduction of Legionella bacteria in the system. If regular flushing is having no effect on the levels of Legionella then all of the existing control procedures need to be reviewed and amended if necessary.
Hot and cold water systems should be designed to aid safe operation by preventing or controlling conditions which permit the growth of Legionella. Flushing procedures should be based on a risk assessment of the water systems in the building/institution concerned. A flushing protocol is only effective where the water system is adequate.

The following are risk factors that should be considered in the risk assessment:

Institutional risk factors

Age and condition of the pipes

Older pipes are more prone to the growth of Legionella because of corrosion, scaling, biofilms and sediment. Legionella bacteria require a supply of nutrients to multiply. Sources of these nutrients include commonly encountered organisms within the water system such as algae, amoebae and other bacteria. The presence of sediment, sludge, scale and other material within the system, together with biofilms, facilitate the growth of Legionella and may provide protection for the Legionella bacteria from temperatures and disinfectants that might otherwise kill or inhibit the growth of these organisms.

Redundant pipe work and fittings

Hospitals are frequently constructed over a long period of time and as a result often contain a considerable amount of redundant pipework/deadlegs

in which water can stagnate which also facilitates the growth of Legionella.59 Studies have shown that flushing of outlets whilst reducing stagnation has little effect on biofilm, particularly when applied to outlets supplied from extensive pipework distribution systems. Therefore, before the procedures are carried out, consideration should be given to the removal of infrequently used sanitary fixtures such as showers and taps, etc. If they are removed then the redundant supply pipework should be cut back as far as the main connection.52 Showers (excluding safety showers) should not be fitted where they are likely to be used less than once per week.

Complexity of the system

Complex, lengthy pipe systems are more at risk than simpler, short systems.

Population at risk

In the hospital setting, patients with predisposing risk factors are not only at higher risk of infection but also have a higher mortality rate when infected with Legionella. Consequently, hospitals and residential institutions must pay particular attention to the prevention of legionellosis. Those at higher risk include:

• Immunocompromised organ transplant patients, patients with HIV/AIDS, and those receiving systemic steroids
• Patients with underlying chronic disease such as diabetes mellitus, congestive heart failure, chronic obstructive pulmonary disease, and chronic renal disease
• People over 50 years of age
• Smokers
• Those with excessive alcohol intake.

Prior history of building

History of legionellosis associated with the building

History of positive water cultures from the potable water system and outlets or cooling towers.

When planning the construction of the water supply system to a building it is essential to minimise the development of biofilms. This can be done by emptying water limbs that are not in service and by preventing water stagnation in the distribution system. Disinfection systems should be in place from the first moment the water flows through the system. Once established, biofilms are extremely difficult to eliminate. In new hot and cold water systems, if more than seven days has elapsed before the system is put into regular use, every outlet should be flushed until the water temperature stabilises.

Thermostatic mixing valves

If water is maintained at 51C (124F) thermostatic mixing valves (TMVs) can be used to prevent scalding.They should be sited as close as possible to the point of use. Ideally, a single TMV should not serve multiple tap outlets but if they are used the mixed pipework should be kept as short as possible. Self-disinfecting TMVs are now available but their effectiveness may be compromised by the presence of extensive sludge, scale and biofilm in the water distribution network.

Zone protection

The risk assessment should also take into consideration whether there is zone protection of the system i.e. whether or not there is a possibility of cross-contamination between different parts of the system. When buildings are being planned or old buildings renovated, zone protection of the water supply system should be included.

Flushing Procedure

The risk from Legionella bacteria growing in peripheral parts of the water system such as deadlegs off the recirculating hot water system may be minimised by regular use of these outlets. Water within the system may stagnate because a particular outlet is not used for more than a week.59 In most hospitals, there are areas which may have water outlets such as showers that are not used for significant periods of time. These areas may change from time to time, as wards or patient bathroom areas are disused and reopened. Showers in such areas are more likely to harbour Legionella than those in areas where outlets are in regular use. Hotel accommodation may present the same problem with bedrooms unused during the off-peak periods.

Showers and water outlets that are in daily use do not require flushing.

How to flush

The frequency and duration of flushing procedures should be based on a risk assessment. Only run showers that are intermittently used. All outlets should be flushed at full flow (the water flow should be increased gradually to minimise the production of aerosols) at least once per week. However, risk assessment may indicate the need for more frequent flushing where there is a more susceptible population present, e.g. in hospitals, nursing homes etc.52 High-risk areas in hospitals e.g. wards with immunocompromised patients, renal transplant units, may require flushing on a daily basis. The local multidisciplinary infection control team should make these decisions. Healthcare facilities

The duration of flushing should be based on a risk assessment but at a minimum the procedure below should be followed:

Showers

Run showers for four minutes weekly as follows:

Run cold for two minutes

Run hot for two minutes once water is hot.

Taps

Run individual hot and cold taps weekly as follows:

Run cold for two minutes

Run hot for two minutes once water is hot.

Mixer taps

Run with the lever in the coldest position for two minutes weekly

Run with the lever in the hottest position for two minutes weekly

Ensure that hot water comes out hot when in the hot position and cold when in the cold position.

Cold water should be used to flush the cold water system and hot water to flush the warm water system. The period of flushing must be sufficient to remove all stagnant water leading to the outlet. The number of outlets that can be flushed simultaneously will depend on the capacity of the water heater and the flow capability of the system

Where it is difficult to carry out weekly flushing, the stagnant and potentially contaminated water from within the shower/tap and associated deadlegs needs to be purged to drain before the appliance is used. It is important that this procedure is carried out with minimum production of aerosols, e.g. additional piping may be used to purge contaminated water to drain. Automatic drain valves fitted to showers to drain the mixer valve and shower hose after use, can produce conditions within the shower that support the growth of Legionella, and are not recommended as a method for controlling the risk of exposure to Legionella

Where a single TMV serves several multiple showerheads, it is important to ensure that these showers are flushed frequently. Where an outlet is not used for more than a week it must be flushed until the temperature of the water at the outlet has reached the pre-determined temperature set by the thermostatic mixing valve. Every thermostatic mixing valve must be cleaned and maintained at least once in every calendar year.

4.15.2 Cleaning and disinfection of showerheads

Consider replacing showerheads and hoses as an alternative to cleaning and disinfection. Dismantle, clean and descale showerheads and hoses quarterly or as necessary. In high-risk areas this should be done on a monthly basis. Disinfectants containing chlorine can be used to disinfect showerheads.However, chlorine concentrations vary in different products.Household bleach can lose some of the chlorine over time so newly manufactured bleach should be used if possible. Thick bleach solutions should never be used for disinfection purposes as they contain potentially poisonous additives.

Monitoring Once started, the flushing procedure has to be sustained and logged as lapses can result in a critical increase in Legionella bacteria density at the outlet. A flushing protocol should be introduced in each institution. The protocol should be incorporated into the institution's regular cleaning contract. A monitoring system must be put in place to monitor compliance with the flushing protocol. Records of compliance should be maintained and a nominated person should be accountable for implementing the protocol and for maintaining records.

Audit
A regular audit of control and monitoring procedures should take place. Precaution Maintenance, cleaning, and operating procedures should be designed to control the risks to staff and others who may be affected. Personnel involved in flushing procedures should be adequately trained in safety procedures including the use and maintenance of personal protective equipment

4.15.3 Recommended inspection frequency and monitoring guidance for risk systems

Hot and cold water systems

Temperature control

Cold water systems should be maintained at a temperature <20C, while hot water should be stored at 60 C and distributed so that it reaches a temperature of 50C within one minute at the outlets. Care is needed to avoid much higher temperatures because of the risk of scalding. At 50C the risk of scalding is small for most people. However, the risk particularly to young children, people who are disabled or elderly and to those with sensory loss will be greater. The risk of scalding also increases rapidly with higher temperatures and for longer exposure times. Where a significant scalding risk has been identified the use of TMVs on baths and showers should be considered to reduce temperature. These need to be placed as close to the point of use as possible.52 Where buildings cannot be retrofitted with TMVs, periodically increasing the temperature to at least 66C at the point of use or chlorination followed by flushing should be considered.