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Richard W Gilpin PhD Blog

Legionella Routine Testing

GTS Legionella Testing Laboratory has tested several thousands of environmental water samples since 1981. 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, and spas.

Some building managers are testing hundreds of cold and hot potable water sites at many locations within buildings belonging their institutions; resulting in considerable cost and no actionable information.

Water treatment companies and legionella testing labs may be partially the blame for pushing their clients to over-test to increase their profits.
When we started commercial legionella testing, it was not unusual to find cooling tower numbers exceeding 100,000/ml by culture or DFA. This is a rare occurrence now.

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 quite low or undetectable in water treatment plant potable water effluent. There are no federal regulations for certification of laboratories testing environmental water samples for legionella. Therefore, over the years, hundreds of laboratories have entered the legionella testing business - minimal training is needed to plate water samples on appropriate agar media and look for colonies.

The Centers for Disease Control and Prevention (CDC) does not recommend routine environmental water testing for legionella, but CMS has recently recommended that hospitals perform surveillance testing. CDC's mission is to save lives and protect people from health threats such as Legionnaires' disease (legionellosis). ASHRAE also avoids routine testing in their 188 standard, although it is mentioned in a normative appendix. But, CDC does recommend testing when 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 causing legionellosis cases.

The environmental source of many outbreaks is not identified. In our opinion, inability to identify environmental sources can be the limitation of the culture method for 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 which inhibits the growth of legionella or overgrows legionella colonies on BCYE agar, with or without supplements. The DFA method appears to be more accurate for these types of samples.

Building owners routinely test cooling towers and other water-containing mechanical equipment to determine whether their legionella control programs are working. They send water samples to labs that use a monoclonal antibody modification of the original CDC direct fluorescent antibody (DFA) test method or they send samples to labs that use the culture test method. The Wisconsin State Laboratory of Hygiene has a voluntary registration process (Elite) for labs that use the culture method, but the culture method has some flaws. 

More outcome research is needed to determine whether routine legionella testing of cooling towers and other water-containing equipment is a useful supplement to the guidelines published by ASHRAE, AIHA, AWT, EPA, CDC and OSHA. It is clear that the legionella testing regulations by the State of New York have not prevented legionellosis outbreaks.

RICHARD W GILPIN PHD