How to test for Legionella in water. Our GTS Legionella Water Testing Service has tested thousands of environmental water samples – Now in our 5th-decade..
In my opinion, today’s Legionella testing methods based on research with potable water supplies are inadequate.
I studied fresh water microorganisms in graduate school; we need environmental microbiology researchers, not engineers, to develop useful Legionella tests for cooling towers. [Click on link to learn how cooling towers operate].
Forty-five-years after the Philadelphia cooling tower outbreak we still do not have testing methods to locate sources of airborne droplets containing Legionella bacteria that people inhale from water-containing mechanical equipment such as cooling towers .
The current agar culture and qPCR genetic marker testing methods find Legionella in potable water samples, but these methods are inadequate when testing samples from water-containing mechanical equipment exposed to dirt in the environment. The tests often produce false negative results caused by the assorted species of microorganisms and organic/inorganic debris found in these water samples. That is why we use a monoclonal antibody DFA test method to quantify Legionella in these water samples.
Most samples typically come from appropriate locations, including hot water faucets or showers far from hot water heaters, hot water heating systems, cooling towers, evaporative condensers, misters, fountains, and spas.
Some building managers request tests for hundreds of cold and hot potable water sites at many locations within buildings belonging to their institutions; resulting in considerable cost and no actionable information.
Water treatment companies and legionella testing organizations may be partially the blame for pushing their clients to over-test these potable water sites to increase their profits.
When we started commercial legionella testing 5-decades ago, it was not unusual to find cooling tower numbers exceeding 100,000/ml.
This is less common now, but cooling towers remain the major source of Legionnaires’ disease outbreaks.
Why Test for Legionella?
Legionella testing validates whether your legionella control procedures are working.
The National Academies of Science [NAS]: Management of Legionella in Water Systems is the best non-biased source of scientific facts on testing, in my opinion.
There are no federal regulations specifying permissible numbers of legionella in water systems.
There are numerous legionella guidelines (so-called standards) in the United States: AIHA, APIC, ASHRAE, AWT, CDC, CMS, CTI, EPA, NSF, OSHA, & VA.
Much effort and money can be wasted by just monitoring physical and chemical parameters of building water systems with no routine, quantitative legionella testing of aerosol-producing warm water-containing sources such as cooling towers, spas, fountains, & hot water lines.
When we find significant numbers of legionella in a water sample, we suggest decontamination using industry-standard procedures such as the State of Wisconsin Department of Health Guidelines as modified by the Cooling Technology Institute and/or procedures from AIHA, APHA, ASHRAE, CDC, EPA, and OSHA.
Our Legionella Water Test Method:
We use a modification of the original CDC quantitative direct fluorescent antibody (DFA) test using monoclonal antibodies to detect 14 serogroups of Legionella pneumophila in water samples.
When requested, we will also test for 15 other Legionella species associated with human disease.
Why We Don’t Use the Culture Method:
Water samples cultured on BCYE agar media often produce no Legionella colonies, even when they are present, because the legionella are overgrown or inhibited by competing microbial flora in the water samples.
This is particularly true for water samples taken from warm water-containing mechanical equipment exposed to the environment such as fountains, cooling towers, & spas.
Legionella water testing organizations using the voluntary CDC Elite Culture Method, now managed by the Wisconsin State Laboratory of Hygiene, often report inaccurate test results; according to a publication from the Veterans Administration.
According to the National Academy of Sciences: “Culture techniques may underestimate the true Legionella risk….”
Legionella Risk Management for Safety Professionals:
Available for download: Our January 2020 Technical Webinar presented at a joint meeting of the Chesapeake Area Biological Safety Association and the Potomac Section of the American Industrial Hygiene Association.
Legionnaires’ disease description;
The 1976 Philadelphia outbreak;
Legionella bacterial physiology & diagnostic methods;
2019 Legionnaires’ disease outbreaks;
Risk reduction procedures; &
The EPA decided in the early 1980’s to not add legionella testing to federal/state environmental laboratory certification programs because legionella numbers were known to be extremely low to undetectable in water treatment plant potable water effluent.
There are no federal regulations for certification of organizations testing environmental water samples for legionella, so there are hundreds of organizations in the legionella testing business plating water samples on BCYE agar and looking for colonies.
The environmental source of many outbreaks is not identified, however cooling towers and demonstration hot tubs at public events are often associated with outbreaks.
In our opinion, inability to identify environmental sources may be related to limitations of the culture method when detecting legionella in cooling towers or other warm water-containing mechanical equipment exposed to the environment.
Water from these sources contains a significant microbial flora that either inhibits the growth of legionella or overgrows legionella colonies on BCYE agar.
Our quantitative monoclonal antibody DFA method appears to be more accurate than culture for samples from warm water-containing mechanical equipment exposed to the environment.
The Centers for Disease Control and Prevention (CDC) does not recommend routine environmental water testing for legionella.
If there are 2 or more legionellosis cases associated with a specific time and place, CDC may be called in to assist state health departments with legionella testing to determine the environmental source of the legionella bacteria.
CMS has recently recommended that hospitals perform surveillance testing.
ASHRAE also sidesteps routine testing in their 188 standard, although it is mentioned in a normative appendix.