Key Points

• 264 cases of Legionnaires’ disease were reported in 2021 among residents of Île-de-France. Of these, 75% (197/264) had at least one risk factor, 263 were hospitalized, and 26 (10%) died.

• The number of reported cases of Legionnaires’ disease among residents of Île-de-France in 2021 was significantly higher than in 2020 (+43%) but remained lower than in 2019 and 2018. The upward trend was observed across all departments in the region.

• The number of Legionnaires’ disease cases saw a sharp resurgence in July 2021 and, to a lesser extent, in August 2021.

• A record proportion of strains (32%) were isolated from cases reported in 2021.

• Risk exposure was reported for 35% of cases. Although travel-related exposures remain the most common, they were significantly lower in 2021.