The Legionnaires' disease surveillance system makes it possible to:

• at the local level, to identify risk exposures, investigate other cases linked to these exposures, and implement appropriate environmental control measures;
• at the national level, to determine the incidence, trends, and key epidemiological characteristics of this disease and to identify clusters of cases;
• at the European level, to identify clusters of cases that may be linked to a common source of exposure during travel, in order to take appropriate preventive measures.

Epidemiological Situation of Legionellosis in France in 2025

In 2025, 1,989 cases of Legionnaires’ disease were reported in France through the notifiable disease reporting system. This number of cases remained generally stable compared to 2024 (+50 cases, +2.6%). Of these 1,989 cases, 37 were residents of the overseas departments and regions, and 33 were foreign nationals diagnosed in France. 
The notification rate for Legionnaires’ disease cases in France was 2.8 per 100,000 inhabitants (2.9 per 100,000 inhabitants in mainland France).

Since 2017, the number of reported Legionnaires’ disease cases has remained high, and the case fatality rate has not decreased. It is therefore essential to maintain a high-quality surveillance system with prompt reporting of all cases, coupled with a systematic and responsive investigation to limit the number of cases that could be linked to a single source of contamination. Furthermore, it is essential to continue promoting the systematic collection of respiratory specimens, which allows for the diagnosis via PCR of cases not caused by Legionella serogroup 1, provides strains for documenting clusters of cases, and—through comparison with environmental strains—enables the identification of probable sources of contamination.