PROSPECTIVE
Author Whiley expounds the view that routine testing of potable water systems for Legionella should be abolished from all guidelines and an emphasis alternatively be placed on maintaining control measures. This view is in direct contrast to the views of the authors(Samuel Collins and Jimmy Walker) detailed below:
According to Collins and Walker it has been well established that a priority in any potable water system must be to establish and monitor appropriate control regimes aimed at limiting both the potential for Legionella to grow and its dissemination. Further to this, risk assessing control strategies forms the basis for many standards worldwide, including the UK Health and Safety Executive Approved Code of Practice L8 and the US ANSI ASHRAE guidelines.
As the authors state, however an over reliance on routine sampling results (which we appreciate only represent a snapshot in time) can induce a false sense of security and so too can an over reliance on control measures alone. To illustrate this point - for three potable water systems who were epidemiologically linked with separate clusters and cases of Legionnaires’ disease (LD), control measures (e.g., temperature, and flow) were within recommended parameters and monitored as per national guidelines. However, extensive Legionella colonisation was present in key areas, notably where hot and cold water was mixed, e.g., post-thermostatic mixing valves and showers (unpublished data). Colonisation and risk were only identified by epidemiological data, i.e., when cases of LD were reported.
Their view is that routine testing at these critical control points would have given an early warning and may have prevented these cases from occurring. The availability of planned routine sampling results can also prove very useful in public health investigations of LD, where the colonisation history of a system under investigation (i.e., epidemiologically linked to cases) can help focus investigations and pin-point sources more readily.
These authors also make reference to health-care facilities where reducing the exposure of vulnerable individuals is a key priority. For most UK hospitals, a zero-tolerance approach to Legionella is based on the assumption that there is no known safe level of Legionella and that remedial actions are therefore implemented at the detection of any concentration of Legionella [7]. Unlike current Centers for Disease Control and Prevention (CDC) recommendations [8], routine testing plays a crucial role in the water safety plan approach to managing these healthcare systems, proactively identifying risk and offering an additional layer of security to prevent even a single case of LD occurring.
This approach, combined with clinical surveillance, has been shown to be effective in identifying and reducing cases of nosocomial LD [9].
With the well acknowledged limitations of Legionella monitoring, is the safest approach a combination of a risk assessment, control measures (including meticulous monitoring), and routine water testing?
LPC Inc agrees with the authors that routine testing should be implemented on a system-by-system basis, informed by the risk assessment to reduce inappropriate or meaningless testing and expenditure and take into account the history of the system, the control measures, the previous test results, the population at risk, etc. The absence and detection of low concentrations of Legionella by culture (or by other analytical methods) combined with verified control measures are the ultimate reassurances that the microbiological risk has been managed appropriately. After all, cases of LD do not tend to be linked to systems where Legionella has not been detected [9,11,12].
At LPC Inc clients are advised that they may include initial testing of the system in the beginning and testing for validation annually or bi annually depending on results and risk categorization. As time goes by the data analysis will provide solid evidence for the reduction in the frequency of testing until you reach a state where detailed continuous monitoring is sufficient.
CEO
LPC Inc, 2019
References
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