WATER QUALITY
Legionella 8 **
VBNC Legionella ***
L. penumophila **
L. penumophila ***
VBNC
Vermamoeba vermiformis
***
6
4
2
0 Low High Low High Low High Low High Low High Statistical significance denoted **p<0.01; ***p<0.001
Figure 4. Relationship between intermittent water usage and the presence of Legionella/Vermamoeba vermiformis. X-axis represents total duration (hours) of flushing events recorded for one-month prior to sampling. Flushing was categorised into low; 0 to <2 hours, and high flow regime; ≥2 to 40 hours. Y-axis represents log10 L. pneumophila, VBNC L. pneumophila, and V. vermiformis (Sourced from Nisar et al 2023).
(GU/L) of Legionella, VBNC Legionella,
vermiformis; however, it did not significantly impact the HPC load. This supports guidelines that recommend routine flushing of outlets to manage Legionella within engineered water systems.10 No associations with temperature were identified. However, as this study averaged water temperatures across one week or one month prior to sampling for both the hot and cold water pipelines/outlets, the water temperatures were more similar to each other than anticipated. This is likely to explain the lack of a statistically significant difference in Legionella concentrations associated with different temperatures. Future research with a larger dataset is needed to explore the temperature relationship further.
Conclusion This study showed that the standard microbiological culture method used to detect Legionella returned a false negative result for 88 per cent of the samples that were found to contain VBNC Legionella. These VBNC Legionella are alive and pose a potential risk to humans. As all samples positive for VBNC Legionella were also qPCR positive, qPCR may be a more appropriate detection method for routine surveillance. However, future research is needed to investigate the concentrations of VBNC Legionella that pose a risk to public health to enable interpretation of these results to inform improved Legionella guidelines. This study also showed that the elimination of temporal
42
water stagnation occurring at outlets through intermittent use is important for the management of Legionella in hospital water systems. This supports the enHealth Guidelines for Legionella control recommendation of routinely flushing outlets. It also demonstrated the use of a real time monitoring system for the management of Legionella that overcomes the limitations with current verification monitoring methods and the demonstrated limitations associated with the standard Legionella detection methods. Ultimately this proactive approach to routine monitoring and water management reduces the risk to end users.
l This article was adapted from: Nisar MA, Ross KE, Brown MH et al. Stagnation arising through intermittent usage is associated with increased viable but non culturable Legionella and amoeba hosts in a hospital water distribution system. Front Cell Infect Microbiol 2023; 13: 1190631 [
https://www.frontiersin.org/ articles/10.3389/fcimb.2023.1190631/full].
References 1 Whiley H. Legionella risk management and control in potable water systems: Argument for the abolishment of routine testing. Int J Environ Res Public Health 2016; 14 (1): 12.
2 Centers for Disease Control and Prevention. Nationally notifiable infectious diseases and conditions, United States: Weekly tables 2022.
3 Australian Government. National communicable diseases surveillance report
fortnight 26, 2020-2021 summary notes for selected diseases 21 December 2020 to 03 January 2021; Department of Health and Aged Care: 2021.
4. The European Legionnaires’ disease Surveillance Network. Surveillance atlas of infectious diseases [
https://atlas.ecdc.europa.eu/ public/
index.aspx].
5. Nisar MA, Ross KE, Brown MH, Bentham R, Whiley H. Water stagnation and flow obstruction reduces the quality of potable water and increases the risk of legionelloses. Front Env Sci-Switz 2020; 8.
IFHE
6. Whiley H, Bentham R, Brown MH. Legionella persistence in manufactured water systems: Pasteurization potentially selecting for thermal tolerance. Front Microbiol 2017; 8: 1330.
7. Abdel-Nour M, Duncan C, Low DE, Guyard C. Biofilms: The stronghold of legionella pneumophila. Int J Mol Sci 2013; 14 (11): 21660-75.
8. Nisar MA, Ross KE, Brown MH, Bentham R, Best G, Whiley H. Detection and enumeration of viable but non-culturable (vbnc) Legionella pneumophila from water samples using flow cytometry-cell sorting and quantitative pcr. Submitted, currently under review 2021.
9. Nisar M, Ross K, Brown M, Bentham R, Hinds J, Whiley H. Molecular screening and characterization of Legionella pneumophila associated free-living amoebae in domestic and hospital water systems. Water Res 2022, 226: 119238.
10. enHealth. Guideline for legionella control in the operation and maintenance of water distribution systems in health and aged care facilities. Australian Government, Ed. 2015.
IFHE DIGEST 2024
log10
(GU/L)
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