Key Points

In 2024, 186 cases of Legionnaires' disease were reported in the Hauts-de-France region.

• The notification rate is 3.3 cases per 100,000 inhabitants, one of the highest rates in the region. It has decreased compared to 2023 but remains higher than in 2022.

• Reporting rates at the departmental level are highest in the Nord (3.8%) and Oise (3.3%) departments, but the highest number of cases is reported in the Nord and Pas-de-Calais departments.

• Case characteristics (predominantly men, median age of 64) are comparable to previous years.

• The case fatality rate is 16.4% (28 deaths), higher than in previous years.

• The diagnosis is made in 95% of cases by urine antigen testing, which remains the most common diagnostic method, supplemented in 30% of cases by PCR.

• A Legionella strain was isolated in 47 cases (25%), leading to a comparison of clinical and environmental strains in 10 cases, 8 of which were found to be identical, allowing the source of contamination to be identified.

• A cluster of nine cases involving individuals residing in or having visited three neighboring municipalities in Pas-de-Calais was investigated.

• The study on sporadic cases of Legionnaires’ disease and household exposure (LEGIODOM) began on October 1, 2024; its objective is to document the proportion attributable to contamination of household water systems, and it will last two years.