Campylobacter and Salmonella infections declined in Switzerland in 2020 while Listeria was stable despite a large outbreak. E. coli reports fell for the first time since 2014.

The COVID-19 pandemic likely influenced disease reports, researchers said. Factors such as resources being diverted to coronavirus, hygiene measures and travel restrictions may explain the trend. The Federal Food Safety and Veterinary Office (FSVO) said people will have to wait until after the pandemic for the situation to be assessed in more detail.

The number of foodborne outbreaks almost halved from 23 in 2019 to 13 in 2020. Overall, 161 people became ill and 36 were hospitalized. Ten deaths were recorded in one incident.

Although the number of campylobacteriosis cases confirmed by laboratory diagnosis decreased from 7,223 to 6,200 it remained the most frequently recorded zoonosis in humans in 2020.

As in previous years, men were slightly more affected than women. This trend was seen in all age groups. There were 1,811 cases between July and August and a second short-lived increase during the holiday season as in past years.

Campylobacter infections exceeded 1,000 colony forming units per gram (CFU/g) for 65 of 780 chicken carcass samples analyzed. Another 118 samples were above the detection limit but were not contaminated at levels as high as 1,000 CFU/g.

Salmonella and E. coli
Salmonellosis remains the second most frequent zoonosis in Switzerland with 1,270 cases in 2020 compared to 1,546 in 2019. The seasonal peaks typical of the summer and fall months recurred again in 2020.

The most frequently reported serovars remained the same with Enteritidis first, followed by Typhimurium and monophasic Typhimurium.

As part of self-monitoring by the poultry sector, 2,794 analyses were carried out on chicken and turkey meat in 2020 and 36 were positive for Salmonella, mostly Salmonella Albany.

The number of confirmed cases of Shiga toxin-producing E. coli (STEC) infections decreased from 999 to 728 in 2020, stopping an increasing trend between 2014 and 2019.

As in 2019, most cases were recorded in the third quarter. With the exception of children younger than 5. Women were slightly more affected than men. A total of 539 cases were reported in women. A possible country of exposure was mentioned in 361 cases with Switzerland listed on 305 occasions.

With 17 cases of hemolytic uremic syndrome (HUS) reported in 2020, the figure was down slightly from 21 in 2019. Seven children younger than 5 and five people aged 65 and over were affected.

Listeria levels
The 58 confirmed listeriosis cases reported in 2020 are within the annual variations usually observed, despite an outbreak in the first half of the year.

As in previous years, the highest reporting rate was recorded in the over 65 age group. Men were slightly more affected than women.

A total of 22 cases were detected between January and July; thanks to whole genome sequencing they were connected with 12 illnesses in 2018 and linked to a cheese factory. Ten people died in this outbreak.

In 2020, 710 samples taken from cheese, milk and environmental tests were analyzed as part of Agroscope’s Listeria Monitoring Program. Listeria monocytogenes was detected in three and other types of Listeria were found in 14 samples.

Other agents
As part of Operation Opson X, run annually by Europol and Interpol on food fraud, Swiss authorities took 15 samples of honey, mostly from Ukraine, to check for the addition of sugars. From 13 samples able to be analyzed, none contained added sugars.

Four confirmed Trichinella cases were identified but the sources of infection were uncertain. It is usually from infection abroad or contaminated imported meat products. More than 2.1 million slaughter pigs and 1,286 horses tested negative for Trichinella. It was not detected in the 7,343 wild boars examined.

One case each of Mycobacterium bovis and Mycobacterium caprae were detected in 2020, both in people older than 75, who likely contracted the disease during their childhood in Switzerland, following consumption of unpasteurized, raw milk, according to the report.

Three cases of lab confirmed brucellosis were reported compared to seven the previous year. Those affected were males aged 2 to 54 years old. Infections usually result from unpasteurized milk products.

In a study published in the journal Pathogens in 2020 by the Institute of Parasitology at the University of Zurich, the genome of Echinococcus multilocularis was detected in two out of 157 lettuce samples.

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