How well do we really understand the multiple factorial parameters that can influence Legionella, Pseudomonas, non-tuberculous mycobacteria, Stenotrophomonas and other waterborne pathogen survival and growth within our in-premise drinking water systems?
Certainly the design of a system and the different materials in the fluid pathway can have an impact, as can the chemical composition of the incoming water. It is clear that the surface attachment of microorganisms and subsequent biofilm formation is influenced not only by the flora contained within our drinking waters, but also by the particulates, formation of scale, flow patterns, supporting and protective structures (e.g. roughness of inner pipe surfaces), corrosion in metallic pipelines, nutrients, temperatures and, if used, systemic biocides. Microorganisms protected within drinking water system biofilms exhibit extreme tolerance to biocide exposure.
Legionella, Pipe Materials and Ions
In order to improve preventative measures and minimise the risk of infection, a Public Health team from Croatia (Rakic et al., 2022) have recently published on whether calcium and magnesium concentrations alongside different pipework construction materials could influence the occurrence of Legionella pneumophila in a hot water distribution system.
The hot water systems of four hotels were sampled over a 12 month period with 108 water samples collected in total and analysed for calcium, magnesium and Legionella pneumophila. Two of the hotels were exclusively plumbed with plastic pipes (PVC) with the other two plumbed with galvanised iron pipe. The public water supply is sourced from underground aquifers with low mineralisation – see summary table below
| Total hardness | Moderate – 11.9-12.3 oD |
| Carbonate hardness | 10.3-11.0 oD |
| Average temperature | 12.3 oC |
| pH | 7.5 |
Following testing, the hotel Legionella results revealed
| Plastic Pipes | Galvanised Pipes | Total | |
| Legionella pneumophila | N=10/56 (17.8%) | N=15/52 (28.8%) | 25/108 (23.1%) |
Hot Water Temperatures Needed at The Point of Use
Unsurprisingly, Legionella contamination was most strongly linked to those hotels that opened seasonally rather than all year round opening, and also to those hotels with cooler hot water temperatures. Where hot water temperatures were < 50 oC at the point of sampling the mean and standard deviation of Legionella counts were 3820 ± 7076 CFU/L vs at 50-60 oC, where Legionella counts were 1000 ± 3075 CFU/L. Where hot water temperatures were > 60 oC at the point of sampling, the results yielded 0 CFU/L. Testing was completed using standard culture method.
Do Galvanised Iron Pipes and Magnesium Ions Stimulate Legionella Growth?
Whilst there was no significant difference in the overall number of positive samples found, when comparing galvanised to plastic pipe materials, there was a significant difference (p=0.034) for the galvanised iron pipe positive samples to have higher levels (> 1000 CFU/L) of Legionella pneumophila contamination. The galvanised pipe samples had significantly higher magnesium levels in the samples, whereas the plastic pipe samples trended for higher calcium levels. The warmest months of the year (July to September) yielded the highest percentage of positive Legionella samples alongside the highest concentrations of magnesium ions. Certain ions can prevent growth and development of cells and biofilms, whereas others have a biostimulatory effect and magnesium is known to support Legionella as an essential nutrient.
Determining risk factors for the presence of Legionella pneumophila and carefully measuring/monitoring them is important to minimise the risk of Legionnaires’ Disease. The authors feel these results are supportive of other similar studies and are helpful for informed decision making regarding protective measures to reduce and eliminate the presence of Legionella pneumophila.
Whilst there is not a high level of galvanised iron pipework in the UK the heightened risk noted with seasonal opening, hot water temperatures and magnesium ions could resonate with many facilities.
Construction Infection Control Risk Assessment
Rakic’s work neatly dovetails with a paper published from a US group who present on an infection control risk assessment tool for water management in design and construction (Scanlon et al., 2022). This multi-disciplinary team consist of individuals from an independent water management company (who do not sell water treatment chemicals or equipment), from public health, architecture and a consultant physician – a great blend of skills and experience to best view hazards, consider risk assessment and understand waterborne pathogens in the built environment.
They remind us that construction activity risk factors associated with in-building drinking water distribution systems include excavation, re-pressurisation, demolition activities, efficiency design (especially cost efficiency), underground utility connections, construction equipment with water reservoirs, water main breaks, vibration activities dislodging biofilms, and especially of concern – poor commissioning of the water system. Construction activity may encompass an entire new build, refurbishment, repurposing or perhaps the installation of a new piece of equipment and maintenance or repair measures.
United States Risk Assessment Tool
In the United States, healthcare facilities are required to implement an Infection Control Risk Assessment (ICRA) for construction activities in order to reduce the risk of hospital-acquired infections (HAI). However their Construction ICRAs focus on airborne pathogens, particularly Aspergillus, and although waterborne pathogens are known to be associated with construction work, they have not been expressly included historically. Water management has previously focused on aggressive mitigation measures such as chemical treatments, or the use of filters as a rapid intervention to protect users. Such control measures are still applicable; however they should rather be part of a total system of risk management for the prevention of waterborne pathogens in building water systems which in the US is called a building water management program (WMP) and internationally referred to as a water safety plan (WSP).
With limited US guidance and tools available to support personnel within healthcare facilities through a risk assessment process, this publication delivers an easy to understand and simple to implement basic Construction ICRA which will help WMP teams to better understand the built environment, extend their hazard and risk assessment through logical approach and ultimately reduce waterborne infection risk.
Despite the myriad of guidance available in the UK and elsewhere in Europe, improvements to any system and plan can be made by embracing new data, thoughts and views, even when in disagreement with them! This document does support holistic thinking and problem solving. The document is freely accessible, so why not take half an hour and read through it –discuss the parts that may be relevant to your construction project with your Water Safety Team. Protection of users from a potentially unsafe water distribution system is essential at any time, including during renovation and construction activities. Tools that support risk management are welcomed.
References
Rakić A, Vukić Lušić D, Jurčev Savičević A. Influence of Metal Concentration and Plumbing Materials on Legionella Contamination. Microorganisms. 2022 May 19;10(5):1051.
Scanlon MM, Gordon JL, Tonozzi AA, Griffin SC. Reducing the Risk of Healthcare Associated Infections from Legionella and Other Waterborne Pathogens Using a Water Management for Construction (WMC) Infection Control Risk Assessment (ICRA) Tool. Infect Dis Rep. 2022 May 6;14(3):341-359