Comparison of the method of quantitative determination of Legionella pneumophila acc. to PN-EN ISO 11731:2017 with the Legiolert™/Quanti-Tray® (IDEXX)

Introduction: Legionella pneumophila is the primary etiological agent of Legionnaires' disease. These are opportunistic pathogens causing lung infections by inhalation of contaminated aerosols. Controlling the presence of these bacteria in domestic distribution water systems (mainly hot water systems) is important for reducing the threat they pose to human health. Legionella pathogens are detected and quantified during routine testing of water samples according to procedures included in PN-EN ISO 11731:2017. However, these procedures are labour-intensive, and the results are obtained after a relatively long time. Implementing the Legiolert™/Quanti-Tray^® test as an alternative method may constitute a good solution: it simplifies the testing procedure and significantly reduces the time necessary to obtain the final result.

Objective: The aim of the study was to compare the relative recovery of Legionella from water samples tested according to PN-EN ISO 11731:2017, and the alternative method of the most probable number (MPN) with the Legiolert™/Quanti-Tray^® (IDEXX) test, and to assess the suitability of the alternative method for routine testing.

Material and methods: Parallel testing was conducted of 38 hot water samples to detect and determine Legionella acc. to PN-EN ISO 11731:2017 and the Legiolert™/Quanti-Tray^® test. Statistical analysis of the results was performed according to PN-EN ISO 17994:2014 and the McNemar's test.

Results: The Legiolert™ test was confirmed to be comparable in performance to the reference standardized method in both qualitative and quantitative detection of L. pneumophila in hot water samples.

Conclusions: The study confirmed that the Legiolert™ test is specific and easy to use, and may constitute an alternative to standardized procedures used in the quantification of L. pneumophila in water.