Basel authorities face probe after Legionella outbreak kills one

Two more people have contracted Legionella in the Swiss canton of Basel-Stadt, bringing the total number of cases to 28. One person has died, and the Basel public prosecutor’s office has opened proceedings on suspicion of negligent homicide, SRF reported.

The new confirmed cases were recorded on Wednesday. Further individual cases could still emerge, said Basel-Stadt Health Director Lukas Engelberger. The incubation period can last up to 10 days.

Melina Bigler of the Swiss Tropical and Public Health Institute said Legionella bacteria can spread over long distances depending on wind conditions. In outbreaks involving cooling towers, they can travel three to six kilometres, she said. The infection risk is very low for healthy people.

Bigler said it was important to monitor and document the spread of the bacteria. This is done in Switzerland, she said.

The danger posed by cooling systems had already been raised in Basel-Stadt in 2018. In a report, the audit commission of the Basel-Stadt Grand Council warned that evaporative cooling systems posed a greater health risk than showers, whirlpools or water pipes. It recommended that the cantonal government maintain a register of such systems and regularly check their maintenance.

Engelberger, who has been in office since 2014, said the canton had investigated the issue at the time. The findings indicated that cantonal rules requiring notification, a register and mandatory inspections would conflict with federal law.

Simon Ming, a spokesperson for the Federal Office of Public Health, said the question of whether cantonal rules would conflict with federal law could remain open in this specific case. The cantons had the necessary tools to carry out routine inspections of evaporative cooling systems, he said.

Engelberger said the canton could act particularly when it identified a health risk. In the current case, the canton closed the facility on Friday, he said.

In 2018, the federal government saw no need for action, according to the audit commission’s report at the time. The Federal Office of Public Health said system owners were responsible for maintaining and refurbishing their facilities. Approval and oversight of ventilation systems, including cooling towers, were left to the cantons. Ming said that position remained valid.

However, the federal government did conduct a research project from 2020 to 2025, involving three federal offices and the cantons. The project examined various questions about Legionella in water pipes and sanitary facilities.

The Basel public prosecutor’s office said it could provide no further information about the criminal investigation, citing official and investigative secrecy, the presumption of innocence and the personal rights of anyone involved in the proceedings.