The Canton of Zürich’s Office of Public Health has raised the alarm over a rising number of Legionnaires’ disease cases, with a notable cluster recorded in the town of Wetzikon. Authorities are urging residents and property managers to adopt basic precautionary measures to reduce the risk of infection.
Infection occurs exclusively through the inhalation of tiny water droplets (aerosols) that may contain Legionella. Human-to-human transmission does not occur.
Legionnaires’ disease, a severe form of pneumonia caused by Legionella bacteria, has been on the rise across Switzerland in recent years, and the Canton of Zürich is no exception. Between 70 and 120 cases are typically registered in the canton each year. Since January 2025, however, 25 cases have been recorded in Wetzikon alone, with the majority of those affected requiring hospitalisation.
Health authorities are taking the Legionella cases in Wetzikon seriously. The Cantonal Medical Service, working alongside the Cantonal Laboratory and other agencies, has launched comprehensive investigations, including detailed patient interviews and analysis of both patient samples and shower water from patients’ homes. Initial test results suggest a possible link between some cases and Legionella detected in shower water samples.
What Is Legionella?
Legionella are bacteria that occur naturally in water. They thrive in conditions where water temperatures sit between roughly 25°C and 45°C and where water stagnates for extended periods, making hot water systems, showers, and other water-bearing installations potential breeding grounds.
Crucially, infection occurs only through the inhalation of tiny water droplets (aerosols), not through drinking contaminated water, and not through person-to-person contact. Those at greatest risk of severe illness include older people, smokers, individuals with chronic lung conditions, and people with weakened immune systems.
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How to Protect Yourself From Rising Legionella Cases
Legionella cannot be eliminated entirely from water systems, but their proliferation can be effectively managed. Authorities recommend the following measures:
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Maintain correct water temperatures — hot water should be stored and distributed at temperatures that inhibit bacterial growth
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Avoid stagnation — do not let water stand unused for more than 72 hours
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Flush pipes thoroughly after any extended period of non-use, such as returning from holiday
Authorities emphasise that consistently applying these measures is the most effective line of defence, as current findings in Wetzikon underline.
