Fewer people were sick but more died in outbreaks in Switzerland in 2023, largely due to a Listeria outbreak with five fatalities, according to a recent report.

A total of 40 outbreaks were reported by Swiss authorities in 2023. More than 260 people fell ill, at least 40 were hospitalized and there were six deaths.

The same number of outbreaks was noted in 2022. While more than 780 people were sickened, only one person died.

Data published by the Federal Food Safety and Veterinary Office (OSAV) and Federal Office of Public Health (OFSP) showed the agent responsible was available for 13 outbreaks in 2023. Three were caused by Salmonella and two were because of norovirus. Histamine, Yersinia enterocolitica, Campylobacter, E. coli, Listeria, and an unnamed parasite all caused one each. The parasite incident sickened three people and was linked to sushi.

Outbreak examples
Two people fell sick after having raw tuna tartare at a restaurant. A sample from a different batch of tuna revealed histamine at a concentration of 10 times higher than the allowed limit. Inspectors found shortcomings in processes, storage of raw fish, and respect of the cold chain.

A group of 26 people were ill with severe diarrhea several hours after eating beef curry at a restaurant. Analysis of the remaining curry did not find any pathogens or toxins. In June, 24 people, including three staff in the same hotel, fell ill with symptoms of diarrhea and abdominal pain. Everyone ate the chicken and mushroom stew served in the restaurant. While no leftovers could be sampled, inspectors found gaps in cooling and storage processes.

In 2023, 74 Listeria monocytogenes infections were reported compared to 78 in the previous year. This was primarily because of a nationwide outbreak with 29 cases, of which six were in 2022 and 23 in 2023. Five people died. The report did not reveal the source but said it was identified with the help of whole genome sequencing and that investigations were ongoing.

As in previous years, the highest reporting rate was recorded in the over 65 age group. From 1,165 tests on cheese, milk and environmental samples, three were positive for Listeria monocytogenes. Other types of Listeria were detected in 21 samples.

E. coli, Salmonella and Campylobacter stats
With 1,224 reported cases in 2023, the rise in Shiga toxin-producing E. coli (STEC) infections stabilized for the first time in recent years. In 2022, 1,208 cases were recorded. The notification rate is the highest since a reporting requirement was introduced in 1999. This increase is mainly driven by new methods that allow more testing to be carried out, which means that patients are more likely to be identified, said Swiss officials.

With 23 cases of HUS reported in 2023, figures remained similar to previous years. Six cases were in children younger than 5 years old and 11 in people older than 65.

For salmonellosis, 1,823 laboratory-confirmed cases were recorded in 2023. This is stable compared with 1,842 infections in the previous year. The top three serovars were the same: Salmonella Enteritidis, followed by Salmonella Typhimurium and monophasic Salmonella Typhimurium.

Switzerland recorded eight patients as part of a multi-country Salmonella Strathcona outbreak with more than 150 cases. Germany had the most cases, followed by Italy. The United States reported eight cases. Of six interviewed people, all of them travelled to Europe before falling sick. While the source is not known, a seasonal produce item, such as tomatoes, is suspected.

Campylobacteriosis was again the most commonly reported agent in humans, with 6,756 laboratory-confirmed cases. This is slightly lower than 7,601 patients in the previous year.

Almost 1,600 cases were reported in July and August. As in previous years, a second peak was observed during the end-of-year holidays.

Campylobacter counts were greater than 1,000 colony forming units per gram (CFU/g) in 101 of 821 chicken carcass samples submitted for analysis. Ninety samples had values between 1,000 and 10,000 CFU/g and 11 were above 10,000 CFU/g.