Whilst temperature is the primary method of microbial control in healthcare building water systems, poor design, inappropriate materials and a lack of effective maintenance results in proliferation of waterborne pathogens and formation of biofilms within the water network. As a result, water sources can present a risk to patients and vulnerable users.
Biocides are often considered an alternative control strategy to reduce the presence of biofilms and waterborne pathogens in healthcare water systems. However, the use and application of biocides must be tailored to each individual building and water system. This article discusses how biocide use does not overcome the inadequacies in design, construction, installation, operation and maintenance and hence they often fail to control the presence of pathogens. Whilst biocides may be seductive, their use and unintended consequences may end in heartbreak.
Operational control of hot and cold water systems in healthcare facilities
Provision of hot and cold water is required in healthcare buildings for cleaning, hand washing, showering, bathing, food preparation, birthing pools and laundry. Hospital water systems are large and complex and whilst water delivered to hospital sites is “wholesome”, once water crosses the threshold, conditions change dramatically which deteriorates water quality.1 Water can be stored in large tanks to maintain a continuous supply to all water services and equipment installed downstream. As outlets are used, water is drawn through pipework which will contain different material types and a range of equipment including calorifiers, expansions vessels, pumps, valves and taps. Water will either be continuously moving or under stasis (not moving) within the pipework. Static water at the periphery of the water system, quickly adopts ambient temperature (typically within 30 minutes even in well insulated pipework). The presence of a large surface area and a combination of temperature changes, stagnant water, aged water and a ready supply of nutrients in extensive and complicated pipework systems are the perfect conditions for microorganism colonisation and growth.
Whilst the majority of microorganisms within a water system are harmless, Legionella spp., Pseudomonas spp., Stenotrophomonas spp., Klebsiella spp., Serratia spp., non-tuberculous mycobacteria, Acinetobacter spp., are recognised as waterborne pathogens commonly associated with healthcare water systems.2 These waterborne pathogens will colonise surfaces and form biofilms consisting of layers of bacteria, amoeba, fungi with associated sediments embedded in a hydrated network.3 As outlets are used, pressure fluctuations release microorganisms and particulates from biofilms into the water stream and contaminating users, equipment and drains. Patients are exposed to pathogens via direct water contact, splashing or aerosolisation leading to outbreaks (healthcare associated waterborne infection).4
Temperature is used for microbial control in water systems. The cold water should be maintained below 20 °C and the hot water calorifier above 60 °C with a minimum of 55 °C at the outlets. The temperature of the return loops should be above 55 °C.5 The detail of consistent temperature control is critical. The goal of cold water temperatures is not simply to maintain the water below 20 °C, but to ensure that there is no more than 2 °C of heat gain between the influent mains water temperature and the furthest outlets. Therefore, if the influent cold water temperature to the building is 14 °C, there should not be more than 16 °C measured at the outlets. Any areas demonstrating greater than 2 °C heat gain in the cold water should be investigated and corrected. Heat gain may be due to inadequate insulation, a cross connection, faulty non-return valve within the hot water system, or extended periods of stagnancy (which is usually due to underuse). Within the hot water system in healthcare buildings, it is common to find hydraulic imbalance, particularly where refurbishment works have added outlets, where areas have been isolated, or where balancing valves have seized. Whilst calorifier temperatures and returns can indicate appropriate and consistent performance, the measurements at the secondary and tertiary loops, and even at the individual outlet level can be vastly different. Pockets of inadequate hot water temperatures (below 55 °C) may be found when forensically analysing the system in detail.5 This activity is difficult to support manually, whereas with continuous remote monitoring the performance of a system can be recorded and diagnosed under periods of rest and peak use with confidence and accuracy.6,7
Other methods to manage microbial contamination are via throughput and turnover. The body of water within a building, representing the total volume in the storage tanks, calorifiers and within the pipe network, should turnover at least daily and ideally more frequently. The detail of turnover is also critical, as this ‘one building volume’ of water should pass through each and every outlet and equipment equally and daily. Recognising outlet and equipment use on a daily basis is no easy task and subject to bias. It is not sufficient to assume that if a room is occupied, then the outlets are regularly used. Known low use outlets are often placed on a flushing list with weekly, twice weekly or daily flushing. However, the efficacy of flushing is rarely verified and consequently the use of intelligent automatic flushing of taps and showers is also helpful to maintain consistency of throughput to outlets which are predicted to be intermittent or low use.
Despite temperature and throughput/turnover being the main control measures, maintaining effective performance of either can be problematic, often resulting in microbial growth. Therefore, a number of secondary control strategies can be risk assessed and deployed. One such secondary control is the use of chemical biocides, such as chlorine derived products, hydrogen peroxide or silver and copper ionisation.8 However, the implementation of a biocide is not a panacea and, in many cases, does not bring about control of waterborne pathogens due to a myriad of survival strategies. In addition, chemicals can have negative or corrosive impacts on materials and surfaces within the water system and may present health risks to consumers from disinfection byproducts.
Biocide efficacy versus environmental persistence of waterborne pathogens
Waterborne pathogens have remarkable environmental adaptability and persistence. Many waterborne microorganisms succumb to impacts of hot water temperature and the application of shock or continuous systemic biocide application. However, tolerant microorganisms will survive and thrive under such conditions. Tolerant microorganisms could be described as “professional” water system dwellers that are capable of biofilm formation, utilising nutrients released from dead cells, hiding and proliferating within other microorganism (protozoa) hosts, and sharing their successful traits with other microorganisms.9,10 Therefore, unless a water system is designed, specified, installed, commissioned and operated continuously under best practice (which is different from compliant with guidance), environmental conditions will prevail which can support pathogen colonisation and amplification.
When introducing a biocide, it is critical to undertake a full risk assessment prior to selection and implementation. A literature search should be undertaken to assess the application of particular biocides under operational conditions reflected at the site under consideration.11-13
The presence of organic matter will negatively impact biocidal performance, particularly in terms of dosage. High organic concentrations will reduce the presence of the active chemistry resulting in concentrations that are too low to control the presence of free-living waterborne bacteria leading to a microbial risk.
It is also important to understand how that organic matter might react, impact and result in the formation of disinfectant byproducts that will result in a health risk to patients.
Microorganisms tolerant to biocide exposure
Equally important is the recognition of how the use of a biocide will select for tolerant organisms, particularly at the concentrations permitted in drinking water systems.14-18 Microorganisms which are tolerant to biocide exposure include waterborne pathogens and populations protected within biofilms or hosts such as protozoa. Whilst much merit is placed on the oxidative action of biocides to penetrate biofilms and enable sloughing, the impact is limited compared to the extent of biofilm formed, and if the operating conditions remain conducive for biofilm formation there is little evidence to suggest that continued use of biocide will prevent biofilm formation. Many studies have reported that there are important caveats in the application of biocides in a drinking water network and prior understanding of a system’s water chemistry along with the operating parameters are critical to determine its effectiveness.19-22
Biocides may select for tolerant organisms which may predispose them to being antibiotic resistance.23-29 Efforts must be made to prevent the selection of antibiotic-resistant strains as healthcare facilities are unable to combat the rise of such infections due to the contamination risks within their built environment from the water and wastewater interfaces. Other control methods do not appear to result in such selective pressures, including UV irradiation, filtration (including point of use filters), physical removal of contaminated componentry and underused outlets which should be preferentially assessed.
Whilst the US, China, Italy and UK have a significant water treatment industry built around the provision of biocides into healthcare and other markets, many other countries either restrict or prohibit the use of secondary systemic biocide within drinking water systems.
Central European countries, such as Germany, have guidance and legislation in place which bans continuous biocidal treatment (both primary and secondary use) unless there is a specific argument behind the need for such treatment.30 Such strategies focus on mandatory compliance with a Code of Practice for water suppliers as well as Dutyholders, and have a strong requirement towards water system design, operation, maintenance and the materials in contact with water. Water suppliers are obliged to provide water to the public water system that does not pose any risk to human health in the absence of disinfectants.30,31
Temperatures between 55 °C and 60 °C in all buildings and cold-water temperatures less than 25 °C must be achieved within 30 seconds at each outlet. Approved materials in contact with water are listed by the Federal Environmental Agency which specifies certifications and installation of devices that are tested for use. In addition, there are mandatory legal requirements for use of outlets within a 72 hour period, annual sampling within public buildings for Legionella and at least every three years for commercially used buildings.30,32-34
German law lists threshold values for chemical substances and physical parameters, and Dutyholders have to provide test results from DIN ISO 17025 accredited laboratories.30
Accordingly, if a water system is designed, maintained and operated according to the Code of Practice, microorganisms should be controlled (< 100 CFU/100ml Legionella spp.) and Legionella concentrations not exceeded during regular mandatory sampling.30,35
The German Drinking Water Ordinance allows Dutyholders to provide drinking water to consumers only when their water systems ‘at least comply with the Code of Practice’. Any deviations from the Code of Practice must be immediately identified and eliminated.30 Successful remediation will be confirmed by extended sampling after three, six and nine months post-remediation.32 Secondary disinfection measures cannot compensate for design or operation engineering defects, nor offer protection to users.
Compliance with the legal requirements is monitored by the Health Authorities: any exceedance of the technical specifications are communicated directly to the Health Authorities by accredited laboratories.30 Dutyholders must immediately complete a Risk Assessment and implement the recommended engineering control measures. Health authorities can request the Risk Assessment and verification results of remedial measures at any time.30 The Health Authorities are also directly involved in outbreaks, particularly within healthcare buildings.
When to implement a systemic biocide strategy
Where there is difficulty in maintaining consistent temperature control in healthcare water systems or a loss of microbial control, it may be prudent to use systemic biocides (Figure 1). There are a number of biocides that could be considered including chlorine, chlorine dioxide, monochloramine, hydrogen peroxide and silver-copper ionisation as secondary control strategies.
However, the effectiveness of biocides is impacted by a number of parameters, including:
- Systemic contamination — if high post-flush microbiological results from outlets spread across a wide location range are present, this will likely indicate systemic contamination. However, if corresponding pre-flush microbiological results are higher, or there are post-flush counts in specific hot spot locations within the building, this will likely indicate a peripheral contamination (investigate components close to the outlet) or a local dead leg, neither of which will be addressed by systemic biocide application.
- Concentration — consistent and sufficient biocide concentrations throughout the water system are required as low concentrations will result in microbial growth.
- Contact time — insufficient contact time will not impact any free-living microorganisms.
- pH value — biocides may have an optimum pH range within which they will be effective, therefore understanding how acidic or alkaline your source water is necessary.
- Temperature — biocides may have an optimum temperature range within which they are effective, and “gassing off” effects may be expected in hot water systems.
- Organic matter — a high concentration of particulate matters, unseen by the human eye, will result in degradation of the biocide concentration as it reacts with organic particulate matter as opposed to microorganisms or biofilms. A silt density index test should be completed to identify the general level of loading, and scanning electron microscopy and energy dispersive spectroscopy can detail the materials present.
- Microbial concentration — high number of microorganisms will degrade the biocide concentration.
- Biofilms — to be effective biocide a must penetrate the biofilm. Some oxidising biocides will impact the surfaces of biofilm, although penetration of thick sticky matrices is usually limited and microorganisms remain viable.
- Stagnant water — hydraulic balance must ensure circulation of hot water, no dead legs or blind ends, and water outlets or plumbed in equipment need to be used or flushed on a regular basis (daily, ideally multi-daily) to maintain appropriate biocide concentration through the periphery of the pipework.
Biocides will have undergone laboratory tests under controlled and reproducible conditions to demonstrate performance, including effectiveness against waterborne pathogens and biofilms under short and long-term contact times. However, there is a difference between the laboratory setting and a healthcare in-premise water system. Similarly, there is a difference between laboratory grown microorganisms versus professional waterborne pathogens recovered from operational water systems. Whilst laboratory validation data is helpful, it should not be the only reference point when considering performance under real-life conditions.
Biocides present a risk when used in healthcare water systems. For example, controls must be in place to prevent chemicals from passing into renal and haemodialysis units as the presence of chemicals in the water provided to these units will lead to fatalities. In addition, biocides result in corrosion and shorten the life span of installed components. As such, biocides should be chosen with care, must comply with the appropriate water regulations and their application must be fully risk assessed.
Summary
Water systems are immensely complex, and microorganisms take advantage of that complexity by multiplying and finding niche environments in which to hide and grow. Whilst temperature is the primary method of control, required temperatures can often be difficult to achieve due to poor design, inadequate construction materials, inappropriate installations and heat loos and gain. Hence, the use of biocides to control the overgrowth of microorganisms appears attractive.
However, the application of biocides must be tailored to every individual building and water system. Biocide use does not overcome the inadequacies in design, construction and maintenance and as such their use can often fail to control the presence of pathogens. The chemical romance may be short-lived.
Dr Cathy Whapham
Dr Cathy Whapham has worked in contamination control for more than 25 years, predominantly alongside clinical microbiologists, infection prevention and hospital engineering teams on water hygiene programs. She has extensive practical experience of critical contamination and waterborne outbreaks within public and private sectors both nationally and internationally, and provides bespoke training and holistic advice on waterborne contamination, prevention and control strategies for in-premise drinking water distribution systems, the periphery of the water system and wastewater interfaces. Alongside her water consultancy, Cathy manages the Tickmore Orchards and raises native breed Ryeland Sheep in Herefordshire.
Dr Jimmy Walker
Dr Jimmy Walker is a water microbiology expert with over 30 years experience. He previously worked for Public Health England where he worked on biofilms, Legionella spp., Pseudomonas aeruginosa and Mycobacteria spp. He also worked with the Department of Health (DH England) and the Health and Safety Executive in writing guidance on water microbiology in healthcare. He contributed to the NETB Guidance on non-nontuberculous mycobacteria (NTM) and other waterborne pathogens. Jimmy is the former Chair of the Central Sterilising Club and has published a practical guide to enable healthcare workers to manage waterborne hazards.
Dr Vicky Katsemi
Dr Vicky Katsemi, MBA is a consultant with 17 years of national and international experience in water hygiene and infection control. She advises healthcare and non-healthcare institutions and industry on the management of water installations, compliance with the national and international regulations, outbreak management and infection control, and the development of Risk Assessments, Water Safety Plans and other legally required documentation. Dr Katsemi also conducts educational workshops and trainings in English, German, and Greek, and regularly presents at international conferences. She is an active member of several societies and working groups, including DGKH, WMS and ESGLI. Based in Frankfurt, Germany, Dr Katsemi collaborates with institutions across Europe and the Middle East.
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