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Is a Proactive Approach to Controlling Legionella in the Environment Justified?

Daniela Glažar Ivče1orcid tiny, Dobrica Rončević1,2orcid tiny, Marina Šantić3*orcid tiny, Arijana Cenov1orcid tiny, Dijana Tomić Linšak1,3orcid tiny, Vladimir Mićović1,2,3orcid tiny, Dražen Lušić2,3,4orcid tiny, Marin Glad1orcid tiny, Davor Ljubas5orcid tiny and Darija Vukić Lušić1orcid tiny

1Teaching Institute of Public Health of Primorje-Gorski Kotar County, Palit 143a, Rijeka, Croatia

2Faculty of Health Studies, University of Rijeka, Viktora Cara Emina 5, 51000 Rijeka, Croatia

3Faculty of Medicine, University of Rijeka, Braće Branchetta 20, 51000 Rijeka, Croatia

4Center for Advanced Computing and Modelling, University of Rijeka, Radmile Matejčić 2, 51000 Rijeka, Croatia

5Department of Water and Environmental Engineering, Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Ivana Lučića 5, Zagreb, Croatia

Article history:

Received: 20 October 2020

Accepted: 24 June 2021 

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Key words:

Legionella pneumophila, environmental surveillance program, legionnaires' disease, preventive approach, drinking water distribution system, health and aged care facilities


Research backgroundLegionella are Gram-negative bacteria that are ubiquitous in the natural environment. Contaminated water in man-made water systems is a potential source of transmission of legionnaires’ disease. The aim of this study is to explore the prevalence of Legionella pneumophila in the drinking water distribution system (DWDS) of Primorje-Gorski Kotar (PGK) County, Croatia, for the period 2013–2019, coupled with the incidence of legionnaires’ disease. A number of L. pneumophila-positive samples (>100 CFU/L), serogroup distribution and the degree of contamination of specific facilities (health and aged care, tourism, and sports) were assessed. Based on the obtained results, the reasoning for the implementation of a mandatory Legionella environmental surveillance program was assessed.

Experimental approachSample testing for Legionella was carried out according to the standard method for enumeration of this bacterium. A heterotrophic plate count (HPC) and Pseudomonas aeruginosa number were analysed along with the basic physicochemical indicators of drinking water quality. The research period was divided into two parts, namely, the 2013–2018 period (before implementation of the prevention program, after the outbreak of legionnaires’ disease), and the year 2019 (proactive approach, no disease cases recorded).

Results and conclusionsDuring the 7-year observation period in PGK County, an increase in the number of samples tested for Legionella was found. An increase in Legionella-positive samples (particularly pronounced during the warmer part of the year) was recorded, along with a growing trend in the number of reported legionnaires’ disease cases. In addition to hot water systems, the risk of Legionella colonisation also applies to cold water systems. Health and aged care facilities appear to be at highest risk. In addition to the higher proportion of positive samples and a higher degree of microbiological load in these facilities, the highest proportion of L. pneumophila SGs 2-14 was identified. Due to the diagnostic limitations of the applied tests, the number of legionnaires’ disease cases is underdiagnosed.

Novelty and scientific contributionThe introduction of a mandatory preventive approach to monitoring Legionella in DWDS water samples, along with the definition of national criteria for the interpretation of the results will create the preconditions for diagnosis and adequate treatment of larger numbers of legionnaires’ disease cases.

*Corresponding author: +38551651267

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