Key Points

In 2020, the number of Legionnaires’ disease cases reported to Santé publique France was lower than the number of cases reported since 2017, representing a 27% decrease compared to the number of cases reported in 2019 but slightly higher than that of 2016. An investigation conducted by the CNR among the six main suppliers of antigen tests suggests that the use of diagnostic testing for Legionnaires’ disease did not decrease in 2020 compared to 2019, as the number of tests distributed was higher (+30%), tests likely performed as part of a differential diagnosis for SARS-CoV-2 infection.

In the context of the SARS-CoV-2 pandemic, the monthly number of cases has been below the monthly average of reported cases from 2010 to 2019 since April 2020, except in October (+6%). This downward trend is also observed at the European level: the provisional European notification rate for 2020 was below 2.0 per 100,000 vs. 2.2 in 2019. Cases of co-infections with Legionella and SARS-CoV-2 were identified and investigated early in the pandemic: 7 cases detected among the 65 cases of legionellosis reported from March 1 to 31, 2020. Co-infected cases were older, more often male, had more comorbidities, and exhibited a higher case fatality rate.

The characteristics of Legionnaires’ disease cases occurring in 2020 are comparable to those of previous years, except for a significant decrease in smoking, either alone or in combination with other risk factors. This downward trend had already been observed in 2019. This trend could be confirmed in the coming years, as the prevalence of smoking in France has been declining in recent years due to the implementation of national tobacco control plans. The proportion of cases with risk exposure (as reported by mandatory notifications) was lower than that usually observed. This decline is primarily driven by the decrease in the proportion of travel-related cases, which was only 13%, due to travel restrictions during the pandemic. In 2020, despite the decrease or stability in regional reporting rates, the west-east gradient in reporting rates observed for many years in France remained present.