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 frequency, trends, and main 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 2024

In 2024, 1,939 cases of Legionnaires’ disease were reported in France through the notifiable disease reporting system. This number of cases was lower than in 2023 (-12%) but comparable to that of 2022. Of these 1,939 cases, 31 were residents of overseas departments and regions, and 16 were foreign nationals diagnosed in France. The case notification rate for Legionnaires’ disease 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 methodical 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 belonging to Legionella serogroup 1 and provides strains for documenting clusters of cases; and, through comparison with environmental strains, to identify probable sources of contamination.