Evaluation of IDEXX Legiolert for In-house Testing of Cooling Tower Water Samples

Current Topics in Microbiology
Oral Presentation

Presented by J. Hunter
Prepared by B. Nayak, B. Nayak
Pinellas County Utilities, 1620 Ridge Rd, Largo, FL, 33778, United States

Contact Information: bnayak@pinellascounty.org; 727-582-2306


Legionella is a bacterium that occurs naturally in soil and aquatic environments. It becomes a health concern when it grows and proliferates in the built (manmade) environment such as cooling towers, premise plumbing, decorative fountains, hot tubs, etc. and is transmitted to susceptible hosts via aerosolization. Routine maintenance and monitoring of building water systems is recommended to reduce the risk of Legionella growth and spread. As part of an ongoing cooling tower (CT) monitoring program, the Pinellas County Utilities (PCU) Water Quality Division (WQD) monitoring technicians collect CT water samples from facilities around the County. For more than a decade, these samples were shipped to a commercial lab for Legionella testing using the CDC method which relies on selective agar for isolation and enumeration of presumptive Legionella isolates. The PCU lab routinely performs IDEXX Enterolert and Colilert tests for regulatory compliance purposes. When IDEXX launched Legiolert for non-potable water, the Laboratory decided to run a side-by-side trial to evaluate the possibility of performing Legionella testing in-house instead of outsourcing to a commercial laboratory only if the Legiolert method demonstrated equivalent or greater sensitivity than the CDC culture method. Both these methods are culture based but the ease of sample processing, elimination of confirmation steps and a faster turnaround time made Legiolert a worthwhile option to explore in terms of providing the service in-house. L. pneumophila was detected in 11 cooling tower water samples using Legiolert during the six month trial while Legionella was detected in 2 samples using the CDC method. Based on the results of this trial, the Legiolert method was observed to be equivalent or more sensitive than the CDC method and the decision was made to test CT water samples in-house using Legiolert.