Legionella in Germany: over 2,200 cases a year, and the trend is rising
The Robert Koch Institute recorded more than 2,200 notified Legionnaires' disease cases for 2024 alone. By comparison, in 2020 the figure was still 1,276, an increase of over 70 % in four years.
And the number of unreported cases? Considerably higher, experts say, because many cases of pneumonia are never even tested for Legionella.
Why now, of all times?
The reasons for the increase are manifold. The population is ageing, and older people are more susceptible to Legionnaires' disease. Summers are getting warmer, which speeds up the growth of Legionella in water systems. And in many buildings, drinking water stagnates in poorly maintained pipes, especially on little-used floors or in holiday flats.
Deutsches Ärzteblatt (the German medical journal) has already called for doctors to test for Legionella in every case of unexplained pneumonia.
Where the problem originates
Legionella need warm, standing water. They preferentially settle in biofilm, in the slime layers that form on pipe walls, in hot water storage tanks and in dead legs. There they are protected and multiply undisturbed. Only when water flows through the tap or comes out of the shower as an aerosol do they reach the airways.
That explains why most infections occur between June and October: higher outdoor temperatures heat up the pipes. The perfect breeding ground.
What helps against Legionella, and what does not
Thermal disinfection (so-called heating to above 70 °C) is one option, but it is energy-intensive and not suitable for all systems. Hydrogen peroxide is used in many buildings; on the list of the German Environment Agency (UBA) under Section 20 of the Drinking Water Ordinance, it is listed only for oxidation, not for disinfection.
biostream®-ZERO chlorine dioxide, by contrast, penetrates the slime layer of biofilm. In 1,620 individual tests at Leibniz University Hannover, biostream® ZERO was shown to be 99.9 % effective at a contact time of just 5 minutes, including against Legionella pneumophila. Its active substance, chlorine dioxide, is included in the list of permitted treatment substances under Section 20 of the Drinking Water Ordinance. And it acts oxidatively on several cell structures at once, not at a single point of attack.
Summer is coming
Anyone responsible for drinking water hygiene in a building, whether as operator, property management or facility manager, should act now. Not only once the water sample shows a problem, but before temperatures rise and the Legionella season begins.
Talk to us. We have been advising building operators, clinics and property managers on fighting Legionella with chlorine dioxide since 2001.