Technical guidance on the control of Legionella in hot and cold water systems
In the draft technical guidance on the control of Legionella in hot and cold water systems -part 2 of HSG274, the ACOP L8 team has allowed a role for rapid testing in Legionella control and management.
This is consistent with the position that the role of rapid testing techniques in Legionella management, is decided on the basis of a risk assessment and a management plan.
The technical guidance covers a range of monitoring situations and opens the possibility of using alternative testing methodologies with all of the advantages of a swift call to action that this type of testing brings.
HOW DOES rapid testing technology work?
Legionella Rapid Test Kits are designed to detect antigen of Legionella bacteria. This innovative methodology was optimised to deliver results on-site in 25 minutes, compared to 10 to 14 days when using traditional testing methods.
It is perfectly reasonable to postulate that a high level of Legionella antigen indicates a high level of Legionella bacteria in the water system. There has been a considerable amount of work done on looking for a correlation between alternative indicators with colony forming units (CFU) as measured by lab culture techniques, but no direct correlation has ever been found.
One of the main reasons no correlation has ever been found is that Legionella is hard to detect by lab culture techniques. The culture methodology is not only complex and slow, but does not detect Legionella when it in its motile phase when Legionella is Viable but non culturable (VBNC).
In the motile phase the bug is looking for a new host and is at its most virulent. During its reproductive phase, which the lab culture technique does detect, Legionella pneumophila, as an obligate intracellular bacterium, is within its amoebic host and unlikely to be present in a water sample taken from a free flowing source. Combined these shortcomings contribute to the low recovery rates reported in the literature for Legionella culture monitoring techniques.
Rapid testing methods overcome these limitations, by measuring the presence of Legionella rather than Legionella reproductive function. Using rapid testing techniques brings significant improvement to the timeliness of alerts and warnings on conformance issues, high risk situations and in outbreak identification, with concomitant improvements in public safety. They are also useful as part of a routine monitoring programme or for checking the effectiveness of a disinfection treatment where a quick on-site assessment has obvious advantages.
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