Key Points

In 2021, the number of Legionnaires’ disease cases reported to Santé publique France was significantly higher (+55%) than the number reported in 2020, a year in which case numbers were heavily impacted by the SARS-CoV-2 pandemic. This trend was also observed at the European level, with a notification rate of 2.4 per 100,000 inhabitants (vs. 1.9 in 2020). It should be noted that eight European countries had a higher notification rate than France in 2021, including Denmark (4.8 per 100,000), which had one of the highest rates, Italy, which recorded the highest number of cases (2,726 cases: 4.6 per 100,000) and Spain with 1,704 cases (3.6 per 100,000).

Although higher than in 2019 (+13%), the number of cases reported in France in 2021 was comparable to that of 2018 (-3%), when a surge in cases—most likely linked to meteorological factors—was observed in June 2018. During the peak observed in July 2021, no clusters of cases were identified, and the hypothesis still accepted to explain this increase was the influence of meteorological factors on the occurrence of Legionnaires’ disease cases, particularly high temperatures, precipitation, and high humidity, which appear to be key factors in the survival and dispersal of Legionella in the environment. In July 2021, the cumulative precipitation for June and July, averaged across France, ranked as the third highest since 1959, with very heavy rainfall in most metropolitan regions except in the Southeast, where precipitation was below average.