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. 2021 Feb;26(7):1900702.
doi: 10.2807/1560-7917.ES.2021.26.7.1900702.

An outbreak investigation of Legionella non- pneumophila Legionnaires' disease in Sweden, April to August 2018: Gardening and use of commercial bagged soil associated with infections

Emma Löf  1   2 , Fanny Chereau  1   2 , Pontus Jureen  1 , Sabina Andersson  1 , Kristina Rizzardi  1 , Petra Edquist  1 , Sharon Kühlmann-Berenzon  1 , Ilias Galanis  1 , Caroline Schönning  1 , Madeleine Kais  3 , Anne Tideholm Nylén  3 , Anders Wallensten  1 , Adam Roth  1 ; National Outbreak Investigation Team  4
Affiliations

An outbreak investigation of Legionella non- pneumophila Legionnaires' disease in Sweden, April to August 2018: Gardening and use of commercial bagged soil associated with infections

Emma Löf et al. Euro Surveill. 2021 Feb.

Abstract

In early June 2018, an increase in non-travel-related cases of Legionella non-pneumophila Legionnaires' disease (LD) was observed in Sweden and a national outbreak investigation was started. Outbreak cases were defined as notified confirmed or probable cases of L. non-pneumophila LD, with symptom onset after 1 April 2018. From April to August 2018, 41 cases were reported, 30 of whom were identified as L. longbeachae. We conducted a case-control study with 27 cases and 182 matched controls. Results from the case-control study indicated that gardening and handling commercial bagged soil, especially dusty dry soil, were associated with disease. L. longbeachae was isolated in soils from cases' homes or gardens, but joint analysis of soil and human specimens did not identify any genetic clonality. Substantial polyclonality was noted between and within soil samples, which made finding a genetic match between soil and human specimens unlikely. Therefore, whole genome sequencing may be of limited use to confirm a specific soil as a vehicle of transmission for L. longbeachae. Handling soil for residential gardening was associated with disease and the isolation of L. longbeachae in different soils provided further evidence for Legionella non-pneumophila infection from soil.

Keywords: Legionella longbeachae; Legionella non-pneumophila; Legionnaires’ disease; case control study; outbreak; soil.

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Conflict of interest statement

Conflict of interest: None declared.

Figures

Figure 1
Figure 1
Distribution of cases diagnosed with Legionella non-pneumophila infection, by month and week of symptom onseta, Sweden, April–August 2018 (n = 41)
Figure 2
Figure 2
Incidence by county (cases/100,000 inhibitants) of cases diagnosed with Legionella non-pneumophila infection, Sweden, April–August 2018 (n = 41)
Figure 3
Figure 3
Selection of cases and controls and stepwise selection of variables for analysis in the Legionella non-pneumophila case–control study, Sweden, April–August 2018 (n = 41 cases)
Figure 4
Figure 4
Minimum spanning tree of confirmed Legionella longbeachae from six cases and seven soil samples, Sweden, April–August 2018 (n = 6 case isolates, n = 17 soil isolates)
See this image and copyright information in PMC

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