WATER SYSTEM SAFETY
temperatures in hot water systems. Legionella responds to stress by entering a viable non-culturable state (VBNC). This means the bacteria is still alive and capable of causing disease, but will not grow in conventional laboratory media. VBNC is an adaptation of many bacteria to environmental stresses such as temperature and disinfectants that commonly induce this response. Figure 2 is a series of charts using molecular-based analytical technique to identify live, dead and VBNC Legionella. The Legionella came from a hot water shower in a large building with a 50˚C hot water supply to the outlet. The Legionella in a suspension was subjected to 55˚C for varying time periods (from 0 to 10 minutes). Without going into the detail of the techniques used, the charts can be understood by following the dots. Purple dots are live Legionella at the start of the experiment, while orange dots are dead Legionella. Green dots are alive but damaged, and will still grow in the laboratory. Blue dots are VBNC. As you can see, this Legionella strain is surviving up to seven minutes at 55˚C. Laboratory culture of the same samples confirmed these results. Note that this is in a suspension in a test tube – not a biofilm in a tap aerator. The VBNC contingent is still able to infect protozoa and cause human disease.
Amoebal cultures
Culture from the same shower water sample also provided some amoebal cultures. Amoebae have been called the ‘trojan horses’ of Legionella, and Acanthamoeba are one of the prime suspects in supporting their multiplication and survival. The amoebae produce temperature and disinfectant-resistant cysts that can shelter Legionella until conditions favour their growth. The images in Figure 3 are of an Acanthamoeba species cultured from the shower. How the interaction between this organisms and Legionella occurs is part of the ongoing work of this study. This suggests that both the Legionella and their amoebic hosts are surviving and multiplying in 50˚C hot water outlets. Clearly, they haven’t read the regulations.
This is interesting science but also good evidence for risk management. What this means for the Estates & Facilities manager is that they can put little confidence in test results being accurate. A positive result certainly means a problem, and is almost undoubtedly an underestimate. A negative result is only reassuring if all the control measures are meeting their targets – but nothing more. On the other hand, the evidence shows that managing the risk by establishing and monitoring control measures (attacking the ‘Trinity’) is the way to go. It will take
26 Health Estate Journal November 2021 5μm
Figure 3: Acanthamoeba trophozoites and cysts (bottom 3 and 4 from left) isolated from a building's shower.
you beyond the compliance-meeting requirement of a negative test result.
Addressing the ‘Unholy Trinity’ Minimising water residency time and maintaining water flow through the building is the ultimate goal of your management strategy. This strategy will unseat the power of the trinity. A three-pronged attack can be used to achieve this goal: n Remove redundancies completely, being careful not to create obstructions and deadlegs in the process.
n Remove obstructions and flow restrictions wherever possible, disinfect them where it is not.
n Ensure turnover of the water through flushing events. Flushing events should be based on water volumes and target outlet temperatures rather than time. Disinfection can be considered when these strategies are in place, as they will permit the best dispersion and penetration of your chosen disinfectant.
Dealing with the issue during the design phase The above strategy is ideally and most cost-effectively dealt with during the design phase. Most of us are not in the design phase, and must tackle the ‘as built’ problem. Some aspects of the trinity are likely to be present in the majority of buildings. Unless identified and controlled they are likely to worsen and possibly multiply with building age. An assessment of the building water system (cold, warm
About the authors
Dr Richard Bentham is associate director at Built Water Solutions – a specialist water treatment company, and Associate Professor, Public Health Microbiology at the College of Science and Engineering at Flinders University in Adelaide, South Australia. Muhammad Atif Nisar is a Postgraduate Research Student at the College, and Dr Harriett Whiley is senior lecturer, Environmental Health, at the same educational establishment.
and hot) with these factors in mind is the first critical step in tackling the issues. A risk-based strategy based on an evidence-based assessment can cost effectively deliver compliance and control. Having such a plan in place builds resilience into the facility management plan. An operational and effective risk management strategy for a healthcare facility’s water supply will cope readily with unforeseen challenges such as a global pandemic.
Further reading n Atif Nisar M, Ross K, Brown H, Bentham R, Whiley H. Legionella pneumophila and protozoan hosts: implications for the control of hospital and potable water systems. Pathogens 2020; 9 (4): 286.
n Atif Nisar M, Ross K, Brown H, Bentham R, Whiley H. Detection and enumeration of viable but non-culturable (VBNC) Legionella pneumophila from water samples using flow cytometry-cell sorting and quantitative PCR. Appl Microbiol Biotechnol 2021. In Press.
n Jones, R, Pope L, Bentham R. Prevalence and nature of Legionella contamination in aged care facilities in Australia. The Australian Hospital Engineer 2016; 39 (2); 20-23.
n Whiley H, Hinds J, Xi J, Bentham R. Real-Time Continuous Surveillance of Temperature and Flow Events Presents a Novel Monitoring Approach for Hospital and Healthcare Water Distribution Systems. Int J Environ Res Public Health 2018; 16 (8): 1332.
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