Legionella Detection in Water Networks as per ISO 11731:2017: Can Different Filter Pore Sizes and Direct Placement on Culture Media Influence Laboratory Results?

Osvalda De Giglio,Roberta Palermo,Giusy Diella,Marina Tesauro,Paolo Trerotoli,Maria Teresa Montagna,Gabriella Serio,Pasqualina Laganà,Michela Consonni

doi:10.3390/ijerph17062077

Abstract

Determination of Legionella concentrations in water networks is useful for predicting legionellosis risks. The standard culture technique using concentration with membranes filters is the most commonly used method for environmental surveillance of Legionella. The aim of this study was to verify whether filtration with different filter pore sizes (0.2 and 0.45 µm) according to (ISO) 11731:2017, followed by directly placing them on culture media, can influence Legionella detection. Three laboratories participated in an experimental study that tested a known suspension of Legionella pneumophila (Lpn) serogroup 1 (ATCC 33152) (approximate final cell density of 15 CFU/mL). E. coli (ATCC 11775) and Pseudomonas aeruginosa (ATCC 25668) were included as control tests. The average (95% CI) percentage of recovery of Lpn was 65% using 0.45-µm filters and 15% using 0.2-µm filters (p < 0.0001). For control tests, the average (95% CI) percentage of recovery was higher with 0.45 vs. 0.2 µm filters: 97% vs. 64% for Escherichia coli (p < 0.00001) and 105% vs. 97% (p = 0.0244) for P. aeruginosa. Our results showed that the 0.45-µm filters provided the greatest detection of Legionella. Because the current national guidelines leave the choice of membrane porosity to the operator, experimental studies are important for directing operators towards a conscious choice to standardize Legionella environmental surveillance methods.

Highlights

Legionnaires’ disease (LD) is a severe and potentially lethal pneumonia caused by the inhalation of aerosolized water from natural and artificial water systems contaminated with Legionella [1,2,3,4,5,6,7,8,9]
Conformity was achieved in 86.7% (39/45) of the plates from 0.45-μm filters and in 0% (0/45) of the plates from 0.2-μm filters (p < 0.0001)
The analysis of concordance by the McNemar test between the filters showed a lack of concordance (p < 0.0001) and a coefficient K = 0 suggesting non-concordance between the membrane filters

Summary

Introduction

Legionnaires’ disease (LD) is a severe and potentially lethal pneumonia caused by the inhalation of aerosolized water from natural and artificial water systems contaminated with Legionella [1,2,3,4,5,6,7,8,9]. Public Health 2020, 17, 2077; doi:10.3390/ijerph17062077 www.mdpi.com/journal/ijerph

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