WATER SYSTEM SAFETY
alone are responsible for 1,400 deaths per year in the US healthcare system.23,39,40 Legionella spp. has also been identified as a leading cause of drinking water outbreaks in the US,41
with annual economic costs
of infections requiring hospitalisation estimated at US $430 m, with costs for NTM estimated to be US $425 m.42 Numerous studies have confirmed a
direct link between OPPPs present in a hospital’s water infrastructure with the organism isolated from the patient using molecular relatedness studies (see Anaisse et al23
for review). Considering the diversity
of opportunistic pathogens known to be present within potable water supplies, and the broad range of illnesses and infections they can cause, it is little wonder that healthcare experts are becoming increasingly concerned with waterborne pathogens in healthcare facilities, with the potential for associated illnesses in healthcare settings enormous.23
Contamination of ‘end-of-line’ plumbing devices Microbial contamination of potable water systems can occur at both distal and proximal to the mains supply in the building water system; however, it is contamination of end-of-line plumbing devices and components, such as taps, aerators, showerheads, and valves, where OPPPs have been found to be far more prevalent relative to the rest of the building plumbing infrastructure.43
End-of-line
fixtures and devices are more likely to present niche microenvironments for organisms to adhere to and colonise, are frequently subjected to heating/cooling of water to levels known to be beneficial to microbial growth, and suffer from stagnation, and lower concentrations of free chlorine relative to regions of the plumbing system more proximal to the building/municipal source supply. The presence of pathogens at these end-of- line locations provides them with a direct avenue of infection for the end-user, making contamination of these locations the highest risk for end-user health. Importantly, it is many of these end- of-line components and fixtures that are most likely to be impacted by the prescribed changes in plumbing materials. OPPPs may enter the premise plumbing system from the mains supply (e.g. L. pneumophilia), or from transfer during hand washing and outlet handling (i.e. P. aeruginosa). After contacting the material surface, the microbes may more permanently adhere to the surface and form (or embed into an existing) biofilm, that protects the cells from attempts at physical and chemical disinfection of the system. The route of exposure to the water outlet user may be via direct contact, ingestion, or aspiration, of contaminated water, or inhalation of contaminated aerosols. Such exposure can cause a
30 Health Estate Journal August 2022
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ACETAL
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Figure 3: Live (green) and dead (red) cell counts from adhered Pseudomonas aeruginosa cells on test polymeric and metallic materials (Acetal, Stainless Steel 304 (SS 304), Stainless Steel 316 (SS 316), Brass Special, and Brass 352). All data points represent data from triplicate samples, and error bars represent 95% confidence intervals around the mean. Cells were stained with Baclight Live/Dead fluorescent stain after 20 hours on the surface, with the number of live and dead cells determined from confocal laser scanning microscope images.
range of serious illness in vulnerable individuals, including skin and soft tissue, respiratory, gastrointestinal, and blood and neurological, pathologies.
Inhibiting bacterial growth As discussed earlier, low-lead copper alloy materials, as well as metal (e.g. stainless steel) and polymer (polypropylene, acetal) alternatives, are already being used to replace traditional brass components found in plumbing fixtures and devices. Several studies have demonstrated that copper and copper alloys, including brass, inhibit the growth of several waterborne pathogens,44, 45
relative to
other ‘more benign’ metals and polymers. For example, studies that compared bacterial adhesion and biofilm formation on stainless steel, PVC, and copper in a simulated plumbing system over 24 days illustrated copper to present the lowest adhered bacterial numbers, followed by PVC, and with stainless steel demonstrating the highest number of adhered bacteria.46 Another study investigated the biofilm
formation potential (BFP) of different plumbing materials (stainless steel, copper, chlorinated polyvinyl chloride, polybutylene, polyethylene, and steel coated with zinc), finding copper to present the lowest BFP for all tests, with stainless steel consistently presenting amongst the greatest BFP of all materials.47
materials – including Pseudomonas spp., Methylobacterium spp., Corynebacterium/ Arthrobacter spp., and Micrococcus spp.48
‘Dramatic differences’ apparent Our own preliminary research into the initial adhesion and growth of the waterborne pathogen, P. aeruginosa, illustrated dramatic differences in the ability for the bacteria to adhere to and colonise the surface of various plumbing materials. After 20 hours’ exposure, bacterial numbers were greatest on Stainless Steel 316, followed by Stainless Steel 304, Acetal co-polymer, low-lead brass, and brass (Figures 2 and 3). The number of live bacteria on Stainless Steel was 212x (316) and 108x (304) greater than that on brass after 20 hours, while bacteria numbers on Acetal copolymer were 80 times greater than brass (Figure 3). Currently available information and studies investigating the role of plumbing material on microbial contamination is, however, limited, and in some cases contradictory.49
There is a Stainless steel materials (304
and 316) have also been demonstrated to readily harbour a range of OPPPs after 12 months in a large building plumbing distribution system, with a mixture of bacteria identified to be growing on the
critical need for future research to provide a comprehensive understanding of the influence of plumbing material on OPPP contamination and end-user exposure, including how water properties and chemistry, stagnation, pH, and temperature, all interact to influence associated risks. It remains unclear as to why the problem of OPPP contamination of potable water infrastructure, and the associated public health risks, have been given a ‘back seat’ relative to other perceived risks for potable water safety. One thing, however, is clear, and that is that the risks of not addressing this problem are significant, and will be magnified with our ageing population,
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