Title: Recent Peer-Reviewed Data on Legionella Testing Methods
Learners will be updated on the most recent research on Legionella testing methods and will understand the key implications of that research.
It is important for water treaters to consider and understand differences in Legionella testing methods. Currently, water treaters are advised to take several factors into account when testing for Legionella, including concentration per sample, the rate of positivity at different sampling sites, which Legionella strains are detected, and occupant susceptibility, among others. The result is a patchwork of information that can be difficult to interpret, even for those with Legionella expertise. One key reason experts recommend collecting all of this data is because traditional methods for Legionella testing are highly variable and inaccurate. In 2011, the CDC found that ELITE laboratories routinely undercounted Legionella concentrations, and another 2017 study identified between 120% and 145% variability between labs. This unfortunate reality decreases confidence in Legionella testing results and can present water treaters with difficult decisions.
Over the past several years there has been significant innovation in the field of Legionella testing methods. New methods have been introduced that deliver more data certainty, allowing for better decision-making. Lateral flow technology, for example, is an on-site method that can deliver a quick presence/absence result for Legionella pneumophila serogroup 1, which can be a useful initial assessment of risk. Molecular methods have a high negative predictive value, meaning there is a very low probability that Legionella is in the water sample when the test comes back negative. While both of these methods can provide useful information for water treaters, the AWT position statement and guidance document suggests that a culture-based test may be preferred for validating a water management plan. Liquid culture is a culture-based test available to laboratories and water treaters that does not suffer from the same issues as traditional methods.
This liquid culture method has been extremely well validated in the field. It has been compared to traditional, plate-based methods in eleven peer reviewed studies and across fifteen global laboratories. These studies evaluated over 1,450 real world samples to reach their conclusions. Several of these studies found the liquid culture method was more sensitive than traditional plate-based methods in both potable and non-potable water. An ISO 13843 study, which determines the performance characteristics of a method, determined that liquid culture demonstrated the best possible repeatability, eliminating the variability that causes so many issues with traditional results. Additionally, the method has been evaluated by two independent method validation groups, including the well-known AFNOR Certification group, and is included as both an ASTM and a UK Bluebook standard method. This presentation will present the data from these studies and will outline the key implications for water treaters.
American Society for Testing Materials (ASTM) International: D8429-21 Standard Test Method for Legionella pneumophila in Water Samples Using Legiolert. December 22, 2021. https://www.astm.org/d8429-21.html
Association Française de normalisation (AFNOR). (2019, June19). The method Legiolert/QuantiTray* Legiolert for water analysis is granted NF Validation by AFNOR Certification as an alternative method to the standards ISO 11731 and NF T90-431 for enumeration of Legionella pneumophila in drinking water and industrial water, under the Certificate number: IDX 33/06-06/19
Association of Water Technologies (AWT). (2019). Legionella 2019: A Position Statement and Guidance Document. Rockville, MD: AWT. Available from https://www.awt.org/pub/?id=035C2942-03BE-3BFF-08C3-4C686FB7395C
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Jeff Bates is the Marketing Manager for IDEXX Water’s Building Water Testing Solutions, which include fast, easy, and accurate tests for Legionella pneumophila and Pseudomonas aeruginosa. Since joining IDEXX Jeff has focused on the public health challenges associated with premise plumbing systems, especially considering recent changes in building usage. Jeff has a B.A. in Environmental Studies from Middlebury College and an MBA from the Darden School of Business at the University of Virginia.