Human infections decline in Norway but pathogens stable in food-producing animals

Most pathogens decreased in 2020 because of the COVID-19 pandemic and reduced travel, according to a report published by the Norwegian Veterinary Institute.

Diseases transmitted between animals and humans are called zoonoses. The decline in humans was highest for campylobacteriosis, salmonellosis and E. coli infections, mainly because of fewer travel associated cases. Occurrence of most pathogens in animals were stable compared to previous years.

It was already known that reported outbreaks halved in 2020 to 23 compared to 46 the year before. Another report found foodborne diseases dropped overall but there were domestic increases for Campylobacter, Cryptosporidium and Yersinia.

Salmonella and Campylobacter infections
The number of reported cases of salmonellosis decreased in 2020 to 440 compared to almost 2,000 in 2019. More than a quarter were caused by Salmonella Enteritidis, followed by other types such as Typhimurium, Newport and Stanley.

In Norway, food-producing animals are only rarely infected with Salmonella. The surveillance program includes testing live animals such as pigs, poultry and cattle and fresh pig and cattle meat.

From 8,882 fecal samples in 1,342 poultry holdings, one broiler flock was positive. One of 3,245 lymph node samples from slaughter pigs was positive. Three out of 2,973 lymph node samples from cattle were positive for Salmonella. A total of 5,905 swab samples of cattle and swine carcasses were examined, and one was positive.

A total of 2,422 cases of campylobacteriosis were reported, of which 1,513 contracted the infection in Norway. For 647 patients the place of infection was unknown. The total was 4,155 in 2019.

The number of people infected in Norway in 2020 was similar to 1,551 infections in 2019. However, at least 200 reported cases in 2019 were part of a large waterborne outbreak. Without these cases, there is a slight increase in domestic infections in 2020, which might be associated with more people spending summer in Norway and in nature because of the travel restrictions. This may have increased the use of untreated or water of poor quality and contact with livestock.

The prevalence of Campylobacter in broilers is low in Norway compared to other countries. Surveillance in poultry showed that 115 flocks were positive for the pathogen.

Carcasses from positive flocks were heat treated or frozen for at least three weeks before being marketed. In total, 1,893 flocks from 490 farms were sampled. Of all farms, 86 had positive flocks and of these, 24 had two or more positive flocks. This means that almost half of the positive flocks originated from less than 5 percent of the farms.

E. coli, Yersinia and Listeria
The number of reported E. coli infection patients decreased to 331 in 2020 compared to 511 in 2019. People developing hemolytic uremic syndrome (HUS) remained low at less than 10 cases per year.

The 83 cases of yersiniosis was a similar figure to that reported in 2019. All infections in 2020 were caused by Yersinia enterocolitica.

Three outbreaks occurred because of Yersinia enterocolitica O:3. The largest was reported in June 2020 with 25 cases. Patient interviews showed 23 people had eaten a pre-washed salad product that contained baby spinach or spinach the week before illness. However, the source of infection could not be confirmed by microbiological testing. The source of the other two outbreaks could not be identified but investigations indicated they were likely a food with a short shelf life and a pre-cut salad product, respectively.

The number of listeriosis cases continues to increase with 37 in 2020 versus 27 in 2019. One outbreak affected four people but the source could not be identified.

Listeria monocytogenes was detected in four sheep. The Institute of Marine Research examined 135 samples of seafood from Norway for Listeria monocytogenes and four were positive, but at less than 100 colony forming units per gram (cfu/g). Another 57 samples of imported fish products were analyzed and four were positive at levels below 100 cfu/g.