The number of foodborne outbreaks and the number of people sick in them fell in Denmark in 2020, according to a report.

A total of 35 foodborne outbreaks were registered compared with 51 in the previous year. The number of people affected was 1,190 with an average of 34 per outbreak and a range of two to 200. Sixteen outbreaks were national and six were international. More than 1,900 people were sick in 2019.

The annual report on zoonoses in Denmark was prepared by the National Food Institute, Technical University of Denmark, Statens Serum Institut, and Danish Veterinary and Food Administration (Fødevarestyrelsen).

Pathogens commonly associated with point-source outbreaks such as norovirus, Clostridium perfringens, and Bacillus cereus decreased in 2020 compared to 2019. General restrictions on gatherings closed restaurants, and increased hygiene focus during the COVID-19 pandemic likely influenced the number of these outbreaks, said the report.

Norovirus outbreaks declined from 19 in 2019 to six in 2020. In late 2019 and early 2020, almost 400 cases of gastroenteritis compatible with norovirus were reported linked to eating oysters from France.

The number of Salmonella outbreaks was stable with 10 in 2020 compared to nine in 2019. Five were caused by Salmonella Typhimurium or the monophasic variant but sources were not found.

The largest national outbreak was due to Salmonella Strathcona with 25 cases from May to July. Imported tomatoes were suspected to be the cause. An outbreak of Salmonella Kottbus occurred in a restaurant in Copenhagen in June. Of 36 patients, 14 were lab-confirmed. Pea purée was the likely source due to cross-contamination and inadequate temperature on a hot summer day.

First report of Enterocytozoon bieneusi
A Campylobacter outbreak affected 161 people within a week in May and ages ranged from 0 to 97 years old. Pasteurized milk was the probable source. A national outbreak with 20 cases was registered from July to December. Campylobacter jejuni, matching the outbreak strain, was detected in five food isolates from Danish-produced chicken, and the dates of positive batches matched the symptom onset of patients. The danish-produced chicken was the likely source.

Denmark reported 19 Hepatitis A infections from May to November in an outbreak initially found by Germany but no source was identified. Imported fresh mint was behind a Shigella outbreak with 44 patients. Lectins, Yersinia enterocolitica, and Shiga toxin-producing E. coli (STEC) also caused outbreaks.

Three small outbreaks of Listeria were identified this past year. Two Danish cases from November were related to an international outbreak. The source was smoked trout from a Danish manufacturer. Another outbreak, with two cases each in 2020 and 2014, was linked to hot-smoked fish products. The last one occurred in December and was national with four cases but a source was not found.

An outbreak in November was caused by Enterocytozoon bieneusi which is a microorganism rarely detected in Denmark and with no outbreaks previously registered in the country. The incident affected 77 people and was linked to a lunch box with various open sandwiches. Most people self-reported the duration of illness up to 14 days. Half of the eight confirmed cases, who responded to a questionnaire sent to staff, reported having been ill for 22 days or more.

Calculating burden of disease
It is known that many people who get sick from something they eat never become part of official statistics. This could be due to them not visiting the doctor or because the doctor doesn’t get a sample that can be submitted for diagnosis.

Without data to show how many people actually get a foodborne illness, it is hard for the authorities to decide where best to allocate resources to ensure consumers have access to safe foods and that as few people as possible become sick from food.

”In order to ensure more accurate data, we continue to apply methods that can correct for underreporting and underdiagnosing – such as during a pandemic – which will allow us to calculate the real burden of disease for various diseases,” said senior researcher Sara Monteiro Pires, from the National Food Institute.

The burden of disease related to six foodborne illnesses was calculated based on 2019 data. Campylobacter, Salmonella, Shiga toxin-producing E. coli, Yersinia enterocolitica, hepatitis A and Listeria monocytogenes were included in the analysis.

At a population level, the burden is greatest for Campylobacter which affects many people but generally, they only have mild illness. At the individual level, it is highest for Listeria monocytogenes, which sickens only a few people, but has a very high mortality rate.

Such estimates are essential to inform food safety policymakers and help establish priorities for ways to reduce the burden. If presented regularly, they can help monitor trends in foodborne disease burden and the impact of implemented interventions said the report.

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