Well, investigations of Legionella outbreaks always seem to involve a combination of microbiology and building science so I thought I would post this link here: BBC News – Edinburgh Legionnaires’ outbreak: Cooling towers ‘likely’ source. I wonder how much Legionella is showing up in other buildings – especially in DNA based surveys – even when people are not getting sick. Where does it lurk? How does it get around?
5 thoughts on “Edinburgh Legionnaires’ outbreak: Cooling towers ‘likely’ source”
Legionella has been shown to be a common isolate from potable water distribution systems, including hospital shower heads and water taps in patient rooms, particularly in rooms which have been unoccupied recently. In addition, Legionella have been isolated in a European study from roadside puddles after a rainstorm. They are likely more widely distributed then first thought. Both the EU and Australia mandate regular testing of cooling towers for Legionella, and specify trigger limits for a disinfection response. No such mandate exists in the USA, although the CDC, ASHRAE (American Society of Heating, Refrigeration, and Air Conditioning Engineers), and the CTI (Cooling Tower Institut e)do have suggested guidelines.
If you read the ASHRAE standardsâ€™, testing for Legionella is not mandated; rather the stress is placed on prevention and proper maintenance of your plumbing systems and cooling towers. Testing for legionella is difficult can easily be missed. In the event that legionella was found in a cooling tower, it still does not mean anything as these bacteria could be dead already from the biocides being used to kill them. The only way to truly test for them is to culture them and that takes 30 days minimum and leaves the public at risk.
Jon: you are correct in that the ASHRAE standards do not mandate testing; neither does the CTI or CDC documents because a mandate can only come from legislative/lawmaking bodies. Testing is suggested, though, otherwise how to know if you have a problem? Viable testing at contract labs (for example, Biosan) has a turnarond time of less then three weeks, and there are both PCR and antibody-based tests available for rapid determination for the presence of pathogenic (serotype 1) Legionella, although, as you point out, they are not indicative of viable pathogens. However, if you have a presumptive positive (rapid) test and a heavily-fouled tower with abundant biofilm, a reasonable person should be thinking about treating that tower as if it had Legionella.
I believe one of the problems with Legionella in particular is that there are many species and serotypes of Legionella, only some of which have pathogenic potential. So it’s very likely that the genus is indeed widespread but in rRNA and metagenomic surveys we aren’t getting enough information to know anything about risk. I believe that the screening in Europe is PCR-based and therefore focuses on the known pathogenic serotypes.
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