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. 2025 Nov;30(45):2500813.
doi: 10.2807/1560-7917.ES.2025.30.45.2500813.

Preliminary report: The most considerable outbreak of Legionnaires' disease in France in the last two decades, Albertville, September 2025

Emmanuelle Vaissière  1 , Audrey Merlet  2 , Muriel Deher  3 , Matthieu Curtil-Dit-Galin  4 , Jean-Marc Yvon  1 , Albane Beaupoil  3 , Emmanuel Forestier  5 , Jean-Marie Kuntzelmann  6 , Brune Joannard  4 , Aymeric Provost  7 , Guillaume Spaccaferri  1 , Christelle Nolibos  3 , Laetitia Beraud  4 , Nathalie Grangeret  8 , Christine Campese  9 , Sophie Jarraud  4 ; Albertville LD Outbreak Team Investigation  10
Collaborators, Affiliations

Preliminary report: The most considerable outbreak of Legionnaires' disease in France in the last two decades, Albertville, September 2025

Emmanuelle Vaissière et al. Euro Surveill. 2025 Nov.

Abstract

In September 2025, 50 laboratory-confirmed cases of Legionnaires' disease (LD) were identified in Albertville, in south-eastern France. Initially, 23 patients were only clinically diagnosed and only confirmed later due to limited sensitivity of the urinary antigen screening test used. All cases occurred within 12 days, suggesting a common point source of massive contamination. Despite investigations and the rapid response of LD surveillance partners, the outbreak source has not yet been identified. Vigilance is maintained to detect possible new cases.

Keywords: Albertville; France; Legionnaires’ Disease; community outbreak; investigation.

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Conflict of interest statement

Conflict of interest: None declared.

Figures

In the chart, cases are shown as squares, which are distributed along the X axis according to symptom onset day. Squares are stacked into vertical bars when cases they represent share the same day of symptom onset. The vertical bar heights are proportional to the number of cases occurring per day, as deducible from the Y axis. Squares are coloured or marked to indicate the diagnostic tests performed on the respective cases. The 50 outbreak cases all had symptom onset between 10 and 22 September 2025. The outbreak peak was on 13 September when 10 cases became ill. All 50 cases had a positive urinary antigen assay for Legionella, with either the K-SeT test from Coris BioConcept, Gembloux, Belgium, or the BinaxNOW Legionella Urinary Antigen Card from Abbott, Illinois, United States. Nine cases additionally tested positive for Legionella by PCR while their culture was negative. In total, 11 separate cases were culture positive for Legionella typed as ST224.
Figure 1
Epidemic curve, diagnostic tests and day of symptom onset of Legionnaires’ disease cases, Albertville, France, September 2025 (n = 50)
The heatmap shows that cases more frequently visited or resided in the western part of the town of Albertville during their incubation period.
Figure 2
Heat map based on the residence and other places attended by Legionnaires’ disease cases during their incubation period, Albertville, France, September 2025 (n = 50)
In the figure, 50 cases of an outbreak of legionellosis are grouped according to the urinary antigen tests, that laboratory-confirmed them. There are three groups. In the first group, 15 cases tested positive for Legionella with the BinaxNOW Legionella Urinary Antigen Card from Abbott only. In the second group, 12 cases tested positive with the K-SeT urinary antigen test from Coris BioConcept only. In the third group, 23 cases tested K-SeT negative but BinaxNOW positive. For each group of cases, any available information on the level of disease severity and other microbiological analyses’ outcomes is described.
Figure 3
Disease severity level and microbiological results in function of urinary antigen test performed, Albertville, France, September 2025 (n = 50)
See this image and copyright information in PMC

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