Over 10,700 cases, including 704 fatalities, were reported in 2021, the ECDC said in its latest Annual Epidemiological Report.

With 2.4 cases per 100,000 population, it was the highest annual notification rate of the disease caused by the Legionella bacteria, it said in a press release. Italy, France, Spain, and Germany accounted for 75% of the reported cases. Males aged 65 years and older were the most affected group, with 8.9 cases per 100,000 population.

The cause of the increased notification rate recently observed in Europe remains unknown, the ECDC said. The bacteria Legionella is found in freshwater environments like lakes and streams. People can get the disease when they breathe in small droplets of water in the air that contain the bacteria. Symptoms appear 2-10 days after exposure.