Abstract
Following an incidence of Legionnaires disease (LD) in 2007, where a municipal shower system was the likely source of infection, Stavanger municipality initiated a surveillance program for Legionella as part of establishing internal risk evaluation and prevention routines. More than 250 shower systems were examined for cultivatable Legionella pneumophila. The prevalence and diversity of serogroups (sg) and sequence types (STs) of L. pneumophila were mapped using available typing techniques over a period of more than 10 years (2010–2021). The surveillance showed an overall reduction in the L. pneumophila colonisation rate in municipal systems from 11 to 4.5% following prevention measures during the period, with the highest colonisation rate in complex systems (e.g., larger nursing homes and sports complexes). Further, an approximately even distribution between sg1 and 2–14 was seen. Whole genome sequencing (WGS) revealed that only a limited number of STs were detected, and they were consistent at specific locations over time. This study showed that environmental surveillance data in combination with available typing techniques and WGS can give the municipality a better tool for risk management and an overview of ST distributions that can be a valuable asset in future source investigations.
Highlights
The Legionella bacteria can cause a severe and potentially fatal form of pneumonia called Legionnaires’ disease (LD) [1]
Approximately 11% (28/256) of the municipal shower systems were culture-positive for L. pneumophila
The prevalence of L. pneumophila varied between 0% and 36% positive systems among the six different building categories
Summary
The Legionella bacteria can cause a severe and potentially fatal form of pneumonia called Legionnaires’ disease (LD) [1]. When the bacteria colonise and multiply in manmade systems with favourable conditions for growth, it may pose a threat to human health through inhalation of bacteria-contaminated aerosols [1,2]. Legionella is an opportunistic pathogen and the elderly or persons with compromised immune systems are at a greater risk of being infected [1]. There are more than 60 known species of Legionella with varying pathogenicity [3]. Legionella pneumophila has been implicated in at least 90% of the reported LD cases (reviewed in [4,5]). L. pneumophila can be subtyped into at least 15 different serogroups (sg) based on surface molecules and into different sequence types (STs), of which there are currently nearly 3000, based on a selected set of seven genes [6–8]. Sequence-based typing (SBT) is crucial for source investigations and epidemiological studies of L. pneumophila. The SBT performed by Sanger sequencing is still considered the gold standard, more recently, whole genome sequencing (WGS) has become the method of choice providing both ST
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