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

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.