Comparison of the qPCR and the HybriScan Legionella Assays vs. Culture for the Identification of Legionella sp. in Non-potable Water Samples

Poster Presentation

Prepared by M. Citriglia, C. Lannan, R. Read
NorthEast Ohio Regional Sewer District, 4747 East 49th Street, Analytical Services, Cuyahoga Heights, OH, 44125, United States

Contact Information:; 216-641-6000


Legionnaire’s disease is a severe form of pneumonia caused by Legionella sp., with the majority of cases due to Legionella pneumophila. Mode of transmission includes the inhalation of contaminated, aerosolized water droplets from man-made water sources such as cooling towers and aspiration of contaminated liquids. Outbreaks and sporadic cases of Legionellosis within communities have been attributed to contaminated, aerosolized water stemming from industrial buildings in close proximity to these communities. In order to evaluate and control the levels of Legionella sp. from these sources, constant monitoring of bacterial levels is recommended. Currently, the gold standard for identification and monitoring of Legionella sp. is by culturing samples onto selective and enriched media. However, this method for Legionella sp. identification has its drawbacks, including long incubation time (up to 10 days), inability to grow viable but non-culturable cells, and the difficulty in confirming serogroup or species. Therefore, it would be of benefit to apply methods for the detection of Legionella sp., in addition to the culture method, that will provide results earlier, and verify the identification of the organism.

Quantitative PCR and the HybriScan Legionella assay are rapid methods for detecting Legionella sp. in water samples. Results from these assays can be obtained within the same day of processing. The qPCR method detects total Legionella DNA from the sample but does not differentiate DNA from live vs. dead cells. The HybriScan assay detects Legionella rRNA by sandwich hybridization. Because rRNA is quickly decomposed in dead cells, the HybriScan assay detects only living cells. Both these methods are currently being employed, in addition to the culture method, by the Analytical Services department of the Northeast Ohio Regional Sewer District on boiler system samples obtained from the wastewater treatment plants. Results from these comparison studies, and their advantages, will be assessed.