Zurich’s health authority has confirmed 33 legionellosis cases in Wetzikon since June 2026, including one death, while investigators say they still haven’t pinpointed a common source of infection despite months of testing.
Since the beginning of 2025, a total of 33 cases of Legionnaires’ disease have been registered in the town of Wetzikon.
The Office for Health (Amt für Gesundheit, AFG) first reported a cluster of Legionnaires’ disease cases in the city of Wetzikon on 25 June 2026. Since then, an interdisciplinary task force involving the Cantonal Medical Service, the Cantonal Laboratory and other specialist units has been running ongoing investigations. Their work includes patient interviews, analysis of patient and shower water samples, and examination of other water-carrying systems and potential sources of infection.
Read More: Basel Legionella Outbreak Reaches 28 Cases
Wetzikon Legionella Cases: What has the testing found so far?
The cases have been spread out across both time and location, with no single cluster point identified. Investigations so far point to a connection between the illnesses and the presence of Legionella bacteria found in shower-water samples in several cases. However, testing of other possible sources has not identified any single common source of infection shared across the cases.
Legionellosis is first and foremost a disease of the respiratory tract.
The AFG says it will continue and, specifically, deepen its investigation into possible sources of infection. Together with the city of Wetzikon, authorities are currently developing an information sheet for building administrators and property owners, summarising recommendations for properly inspecting and safely operating household water installations. The city of Wetzikon also plans a renewed, broad public-awareness campaign reminding residents of recommended precautionary measures.
Case Outcomes: One Death, All Hospitalisations Resolved
The person who died was of middle age and had several pre-existing conditions. Where that person contracted the infection remains unclear and is still under investigation. All patients who required hospital treatment have since been discharged.
No New Precautions Needed, Authorities Say
Despite the ongoing investigation, the AFG states there are currently no new recommendations for the public. The previously communicated general precautionary measures against legionella remain in effect. Officials specifically emphasize that Wetzikon’s drinking water can be consumed without concern, since legionella infection does not occur through drinking water — the bacteria typically spread via inhaled water droplets, such as from showers, rather than by swallowing water.
The health office reiterates that residents and property owners should pay particular attention to household water installations, especially hot-water systems, following the previously issued precautionary recommendations.
