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. 2024 May;29(20):2300506.
doi: 10.2807/1560-7917.ES.2024.29.20.2300506.

An outbreak of Legionnaires' disease linked to a municipal and industrial wastewater treatment plant, The Netherlands, September-October 2022

Roan Pijnacker  1   2 , Petra Brandsema  1 , Sjoerd Euser  3 , Ali Vahidnia  3 , Arnold Kuiter  4 , Jesse Limaheluw  1 , Christine Schout  2 , Gaaled Haj Mohammad  2 , Stijn Raven  2
Affiliations

An outbreak of Legionnaires' disease linked to a municipal and industrial wastewater treatment plant, The Netherlands, September-October 2022

Roan Pijnacker et al. Euro Surveill. 2024 May.

Abstract

Wastewater treatment plants (WWTPs) are increasingly identified as Legionnaires' disease (LD) sources. An outbreak investigation was initiated following five LD cases reported in September 2022 in Houten, the Netherlands. Case identification was based on the European LD case definition, with symptom onset from 1 September 2022, residence in or within 5 km of Houten, or visit to Houten within the incubation period, without other likely sources. We sampled potential sources and genotyped environmental and clinical isolates. We identified 15 LD cases with onset between 13 September and 23 October 2022. A spatial source identification and wind direction model suggested an industrial (iWWTP) and a municipal WWTP (mWWTP) as potential sources, with the first discharging water into the latter. Both tested positive for Legionella pneumophila serogroups 1 and 6 with multiple sequence types (ST). We detected L. pneumophila sg1 ST42 in the mWWTP, matching with one of three available clinical isolates. Following control measures at the WWTPs, no further cases were observed. This outbreak underlines that municipal and industrial WWTPs can play an important role in community LD cases and outbreaks, especially those with favourable conditions for Legionella growth and dissemination, or even non-favourable conditions for growth but with the influx of contaminated water.

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Conflict of interest statement

Conflict of interest: None declared.

Figures

Figure 1
Figure 1
Number of confirmed and suspected Legionnaires’ disease outbreak cases by day of illness onset, Houten, the Netherlands, September–October 2022 (n = 15)
Figure 2
Figure 2
Minimum spanning tree based on 1,521 core genome sequencing typing targets of clinical (n = 3) and environmental (n = 8) isolates related to the Legionnaires’ disease outbreak in Houten, the Netherlands, September–October 2022, as well as randomly selected non-outbreak isolates for context of ST42 (n = 5) and ST82 (n = 4)
Figure 3
Figure 3
Map of normalised measure of risk for Legionnaires’ disease based on the residential address of confirmed and suspected Legionnaires’ disease cases, Houten, the Netherlands, September 2022–October 2022 (n = 15)
Figure 4
Figure 4
Rose plots of the direction of each possible source locations from the residential address of Legionnaires’ disease cases, indicated by the centre of the rose plot, Houten, the Netherlands, September–October 2022 (n = 15)
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