What is Legionnaires' disease?

Legionellosis is a lung infection caused by a bacterium called Legionella. This bacterium is found in the natural environment and can proliferate in artificial water systems when conditions are favorable for its growth, particularly between 25 and 45°C.

Infection occurs primarily through the respiratory tract, by inhaling contaminated water dispersed as an aerosol. Legionellosis begins with flu-like symptoms accompanied by fever, which progresses to pneumonia. It primarily affects adults and particularly impacts individuals with risk factors such as advanced age, smoking, chronic respiratory diseases, diabetes, immune disorders, and immunosuppressive treatments.

It is a notifiable disease that requires prompt and appropriate medical care.

• Learn more about the disease

• Learn more about reportable diseases

A decline in the number of reported cases of Legionnaires' disease in 2020

Key points

• 1,328 cases of Legionnaires' disease were reported in France, compared to 1,816 cases in 2019, representing a 27% decrease. Among them:

  • 12 cases involving residents of the French overseas departments and regions (10 cases in Réunion, 1 in Guadeloupe, and 1 in Martinique),

  • 13 cases involving foreign nationals diagnosed in France.

• The case notification rate for Legionnaires' disease in mainland France was 2.0 per 100,000 inhabitants.

Key Takeaways

The downward trend in the number of cases between 2019 and 2020 should be viewed in light of the specific context of the COVID-19 pandemic in France and worldwide. Indeed, lockdowns and the implementation of preventive measures among the population likely affected the dynamics of Legionnaires’ disease outbreaks in the country.

However, the number of reported cases remains high and underscores the importance of reporting and conducting a methodical and prompt investigation of all cases to limit the number of cases that could be linked to a single source of contamination.