A recent Danish report outlines the foodborne illness outbreaks that occurred in Denmark in 2021. The report was produced by the Danish National Food Institute, the Technical University of Denmark, the Danish Veterinary and Food Administration, and the Statens Serum Institut.

According to the report, there were a total of 63 foodborne illness outbreaks in 2021, with a total of 1,257 case patients and an average of 20 patients per outbreak. Of the 63 outbreaks in 2021, 34 were local or regional, and 29 were national, six of which were part of international outbreaks.

2021 saw an increase in the number of foodborne illness outbreaks in Denmark compared to 2020, during which 35 outbreaks were recorded. The report notes the possibility of the precautionary measures that were put in place during the COVID-19 pandemic being the cause of 2020’s low number of outbreaks.

The report provides a breakdown of Denmark’s 63 foodborne illness outbreaks by their associated pathogens, which are listed as follows:

• Norovirus (22.2 percent)
• Salmonella (19 percent)
• Listeria monocytogenes (7.9 percent)
• Shiga toxin-producing Escherichia coli, also known as STEC (7.9 percent)
• Campylobacter (4.8 percent)
• Clostridium perfringens (4.8 percent)
• Shigella sonnei (4.8 percent)
• Yersinia enterocolitica (3.2 percent)
• Lectins (3.2 percent)
• Enteroinvasive E. coli, also known as EIEC (1.6 percent)
• Enterotoxigenic E. coli, also known as ETEC (1.6 percent)
• Clostridium botulinum (1.6 percent)
• Staphylococcus aureus (1.6 percent)
• Bacillus cereus (1.6 percent)
• Mixed pathogens (3.2 percent)
• Unknown (11 percent).

Norovirus was the most frequent cause of Danish foodborne illness outbreaks in 2021, accounting for 14 outbreaks that affected 493 patients. The most common transmission route that was observed for norovirus was contamination from infected kitchen staff, with 14 outbreaks and 493 people affected.

Using whole genome sequencing (WGS), Salmonella was linked to 12 foodborne illness outbreaks, half of which were part of international outbreaks. Outbreaks associated with Salmonella include sugar melons contaminated with S. Braenderup that spanned 14 countries (41 recorded cases), sesame-based products contaminated with several Salmonella enterica serotypes (12 recorded cases), foreign eggs and egg products contaminated with S. Enteritidis (seven recorded cases), Danish eggs contaminated with Salmonella (26 recorded cases), and psyllium seed husks contaminated with S. Typhimurium (54 recorded cases).

The report also highlights three outbreaks of Campylobacter jejuni that were registered in Denmark in 2021. One long-lasting outbreak with 19 recorded cases was linked to C. jejuni ST21#7. Another outbreak of 28 cases was caused by C. jejuni ST52#4 and ST52#5. The third outbreak included 16 cases of C. jejuni ST50#18. All three outbreaks were revealed by comparison of recent findings in a Danish Campylobacter control program focused on domestic broiler meat.

Finally, the report discusses several miscellaneous outbreaks of interest. There were three L. monocytogenes outbreaks in Denmark during 2021 totaling 10–14 cases that could not be attributed to a source product. Additionally, in November 2021, the first national outbreak of EIEC was detected in Denmark, which resulted in 88 cases, 26 hospitalizations, and three deaths. Traceback investigations pointed to spring onions from Egypt as the possible cause of the outbreak. The report notes the importance of early communication, data access, and WGS in outbreak investigations.