Photo taken on Dec 8, 2022 shows an exterior view of the headquarters of the European Centre for Disease Prevention and Control (ECDC) in Stockholm, Sweden. (PHOTO / XINHUA)

STOCKHOLM – European authorities must be vigilant in detecting and monitoring outbreaks of Legionnaires' disease, a form of pneumonia that has seen a surge to unprecedented levels in the European Union and the European Economic Area, the European Centre for Disease Prevention and Control (ECDC) said on Monday.

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, Legionnaires' disease was the highest annual notification rate of the disease caused by the Legionella bacteria, the European Centre for Disease Prevention and Control said in a press release

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.

Four countries — Italy, France, Spain, and Germany — accounted for 75 percent of the reported cases, the ECDC said.

Males aged 65 years and older were the most affected group, with 8.9 cases per 100,000 population.

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"The cause of the increased notification rate recently observed in Europe remains unknown," the ECDC said, identifying changes in national testing policies and surveillance systems and an ageing population as possible factors.

Changes in the design and infrastructure of water systems, as well as climate and weather changes that may "impact both the ecology of Legionella in the environment and the exposure to water aerosols containing the bacteria" may also have contributed to the increase, the ECDC said.

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Water temperatures between 25 and 42 C and stagnant water are favorable conditions for Legionella growth. "Given the relatively high mortality rate and challenges in identifying and controlling environmental sources, it is crucial that public health authorities remain vigilant in detecting clusters and outbreaks through surveillance," the ECDC said.