Key Points

• In 2025, 338 cases of Legionnaires’ disease were reported in the Auvergne-Rhône-Alpes region.
• The notification rate was 4.1 cases per 100,000 residents, making it the region with the highest notification rate. It has increased compared to 2024 but remains unchanged from 2023.
• Significant disparities exist between departments, with higher reporting rates in the eastern departments of the region.
• The characteristics of the cases (predominantly men, median age of 67) were comparable to those of previous years.
• The case fatality rate was 7.2% (24 deaths), comparable to previous years.
• The use of PCR testing on respiratory specimens has been rising sharply for several years (42% of cases tested positive by PCR in 2025).
• A Legionella strain was isolated in 89 cases (26%, a proportion stable compared to previous years), leading to a comparison of clinical and environmental strains in 12 cases, 7 of which were found to be identical, allowing the source of contamination to be identified.
• Risk exposure was reported in 46% of cases.
• A major cluster of 50 cases was investigated in Savoie.