Legionella Testing Advice for Cooling Tower Operators
Testing for Legionnaires’ disease bacteria (LDB) validates whether legionella amplification (growth) is being controlled by cooling tower maintenance procedures. Read more>
The Occupational Safety and Health Administration (OSHA) is the best source for advice, in our opinion. “The OSHA suggested guideline for LDB concentration in cooling towers, evaporative condensers, and fluid coolers is less than 10 CFU per milliliter. If water concentrations exceed 10 CFU per milliliter or LDB were detected in other samples, take steps to identify the source of contamination or amplification and treat the system. Sample the water system monthly until the source of contamination is identified and adequately treated.” Read more>
The Centers for Disease Control and Prevention (CDC) treats Legionnaires’ disease as an epidemiology issue after two or more cases of Legionnaires’ disease are diagnosed. “CDC is only involved in legionellosis outbreak investigations when additional assistance is requested. State and local health departments are the best source of information for a specific outbreak.” Read more>
"Although the CDC strategy of testing after an outbreak works well for person-to-person transmissible diseases where the source of the disease is another infected individual, it is not well suited to situations in which the source of disease is in the environment.” Read more>
Legionella Environmental Testing Laboratory Licensing:
There are no required federal or state licensing programs for laboratories that perform legionella testing of environmental samples, except for cooling towers in the State of New York. Some Wisconsin State Laboratory of Hygiene Elite labs have reported erroneous high numbers of legionella to their clients with the recommendation that costly emergency legionella decontamination procedures begin immediately. Read more>
Culture Method Issues:
Legionella from warm water-containing mechanical equipment exposed to the environment such as fountains, cooling towers, and saunas cultured on BCYE agar media are often overgrown or growth-inhibited by competing microbial flora that mask the presence of legionella colonies. Culture on BCYE agar with or without supplements, antimicrobial agents, water sample heat or acid treatment lacks the sensitivity of our quantitative direct fluorescent monoclonal antibody (DFA) test. Others have also reported issues with the culture method: (Fields BS, et al. Legionella and Legionnaires' disease: 25 years of investigation. Clin Microbiol Rev. 15:506-26, 2002) (Bartram J, et al. Legionella and the prevention of legionellosis. Geneva: World Health Organization; 2007) (Parthuisot, N, et al. Total and Viable Legionella pneumophila Cells in Hot and Natural Waters as Measured by Immunofluorescence-Based Assays and Solid Phase Cytometry. Applied and Environmental Microbiology 77:6225-6232, September 2011). Culture methods do not detect viable but non-culturable legionella that can cause disease. Read more>
Current challenges to environmental testing for Legionella include the following:
• Despite a number of published procedures for the detection of Legionella in water samples, standard culture methods remain limited by their sensitivity and unreliability in detecting a wide range of Legionella spp. on a consistent basis (Buse, H.Y., et al. Legionellae in engineered systems and use of quantitative microbial risk assessment to predict exposure. Water Research, 46: 921-933, 2012) and detecting VBNC Legionella (Oliver, J.D. 2010. Recent findings on the viable but nonculturable state in pathogenic bacteria. FEMS Microbiology Reviews, 34: 415-425, 2010). Further, the time it takes to receive results limits the utility of testing.
• Wide fluctuations occur in Legionella testing results from the same tap on a daily basis and from the same water sample between laboratories (Lucas, C.E., et al. Accuracy and precision of Legionella isolation by US laboratories in the ELITE program pilot study. Water Research, 45: 4428-4436, 2011).
• There is a lack of standardized protocols for the selection of sampling sites and the frequency of sampling (Bartram, J., et al. Legionella and the prevention of legionellosis. 1st edition, World Health Organization, Geneva, Switzerland, 2007). Read more>