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Legionella sampling procedure

Legionella sampling procedure

Legionella sampling procedure

(OP)
Hi All:

In a property close to ours there was recently a confirmed Legionellosis case.
Further analysis to the water systems on that property cleared it as the Legionella source.
Either way, given the local media exposure, this triggered a full bezerk mode in our top management and they requested a full review of our own Legionella control procedures and to check for potential gaps.
After the internal audit, things looked pretty good on our side and the control mechanisms that we have in place are fairly robust.
Nevertheless, during the course of the audit, one of our engineers gave the suggestion to make combine samples of several locations, run lab tests on those and only if it came back positive, drill down on the actual location. This would allow a significative expansion on Legionella lab samples without blowing through the budget.
For instance, instead of testing just a few HVAC condensate drain pans or humidifiers, take a combined sample of several (say 10 AHUs) and lab test it. If it comes down positive, then repeat individual tests for the AHUs to find out which one(s) is(are) contaminated.
I confess that I never heard of this approach and in my search through international standards regarding Legionella control (UK, US and others) I couldn't find any reference to it, so I'm a little bit lost on this one. It's an interesting idea especially in a property like ours where water lab tests run close to 100kUSD/year and Legionella has a huge influence on this tab.

Does anybody have experience with this approach or any thoughts on this?

RE: Legionella sampling procedure

No personal experience, but it was suggested early on in the COVID pandemic when testing was in short supply. As positivity rate goes up the efficiency goes down, with worst case being all infected, but as a first cut grouped sample is a time saver.

As long as all samples go into tests so none can be missed and followup is done to deal with the group, either by testing all the members or de-contaminating all the members it doesn't seem like a problem.

RE: Legionella sampling procedure

(OP)
Yes, I know that for COVID this approach was taken, but I believe that the method was different. They would just put a bunch of swabs in a reagent to see if there was any change of colour. In that case, there was no sample dilution. In this proposed case, the test sample to be cultured would be a mix of several (say a 10x100ml sample) which I'm afraid could lead to false negatives as one bordeline positive would be diluted by a factor of 10...

RE: Legionella sampling procedure

Take a look at ASHRAE Standard 188-2018 and/or ASHRAE Guideline 12-2020.

RE: Legionella sampling procedure

UK HSE references and guidelines in legionella are some of the best worldwide and they are free!
https://www.hse.gov.uk/legionnaires/index.htm
However if you need for specific use, you would need to reference to British Standards, and those are quite expensive.

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