Researchers have highlighted increased foodborne outbreaks in Switzerland in the past 15 years.

Foodborne outbreaks in the country are identified by cantonal authorities and reported to the Federal Food Safety and Veterinary Office (FSVO). Between 2007 and 2021, 200 outbreaks were recorded. The highest amount during the study period was in 2021, and the lowest was in 2012.

At least 4,668 people fell ill, 303 were hospitalized, and 18 died. The top pathogens detected were Salmonella, Campylobacter, norovirus, and coagulase-positive staphylococci. Other incidents were caused by Scombroid poisoning, Bacillus, Listeria, and Clostridium perfringens.

Outbreaks took place in restaurants, canteens and catering sites, private households, kindergartens and schools, and takeaway establishments, according to the study published in the Journal of Consumer Protection and Food Safety.

Food items reported concerning outbreaks included mixed products (such as composite meals), fish and fish products, milk and milk products, and meat and meat products.

Missing data and outbreak examples

In almost half of the outbreaks, neither a causative pathogen nor an agent could be identified. In around a third of epidemics, no causative food could be identified.

Fourteen of the 18 deaths were attributed to Listeria monocytogenes. Two were caused by the Hepatitis E virus, and one by Campylobacter and norovirus.

One-off incidents had a big impact on the figures. In 2015, drinking water contaminated with norovirus led to 1,194 illnesses and five hospitalizations. This outbreak was used to test the extent to which social media could be used for early outbreak identification.

Another contaminated drinking water outbreak occurred in 2008; Campylobacter jejuni was identified as the pathogen. In total, 185 people fell ill, and one person was hospitalized.

A nationwide listeriosis outbreak in 2020 was traced to a cheese factory. Whole genome sequencing (WGS) was crucial in showing the close relationship between isolates from a cheese sample and the environment and linking 2018 cases to the 2020 outbreak. Overall, 34 people became ill, and ten died.

An increase in hepatitis E (HEV) cases from January to May 2021 was seen, with 105 infections reported across Switzerland. From nearly 200 samples, two pork livers and three cooked sausages were HEV-positive by PCR. Sequencing virus isolates was only possible with a pig liver, which did not match human samples, so no source of infection was identified.

“The trend of outbreaks is increasing and is expected to continue to rise with new molecular biological typing methods such as WGS,” said researchers.

However, there are challenges with doing detailed epidemiological studies at the local level. These include a lack of human or technical resources, conflicting public health priorities, late detection of outbreaks, and a lack of experience in conducting such studies. This means many outbreaks cannot be traced back and solved.

To manage foodborne outbreaks, the FSVO provides a toolbox for cantonal food control and health authorities called ALEK that includes a website, a practical guide and a set of four manuals for different scenarios.

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