An outbreak of hepatitis A in Norway has been linked to imported frozen raspberries.

The Norwegian Institute of Public Health (FHI) and Norwegian Food Safety Authority (Mattilsynet) reported 20 people had been affected but the incident was now likely over.

The outbreak ran from April to October and was reported earlier this year when 10 people were affected.

Of the 20 infected, 18 have been confirmed and two are probable. Most are adults, but the age range is from 10 to 80 years old, and 65 percent are men. In total, 16 people were hospitalized but no deaths were reported.

Nine affected people live in Viken, four in Oslo, three in Vestfold og Telemark, two in Trøndelag and one each in Møre og Romsdal and Innlandet. None had traveled abroad.

There have also been a few cases of the same IA genotype reported from other countries in Europe.

An analysis of patient interviews and purchase information by the Norwegian Institute of Public Health found that 18 of the 20 sick people ate fresh or frozen berries of one type or another. Half of them had eaten frozen, imported raspberries from the same supplier, two to six weeks before illness.

Berries from Bulgaria and Poland were used in various products such as cakes and raw frozen jam, where berries and sugar are mixed into a jam and frozen without heat treatment, then purchased from different bakeries and cafes.

However, there were no potentially implicated berries remaining so it has not been possible to confirm the source of infection by finding the virus in food samples.

Advice to boil frozen berries
The time from being infected with the hepatitis A virus to becoming ill can be up to six weeks. This long incubation period makes identifying a common source of infection particularly complicated, said health officials.

Based on information given to the Norwegian Food Safety Authority, there shouldn’t be any of the berries suspected to be contaminated left on the market.

The agency advises that frozen berries should be boiled for one minute before being used in dishes that are not going to be heat treated, as this will kill the virus.

The last foodborne outbreak of hepatitis A in Norway in 2014 affected about 20 people and it was also linked to frozen berries.

Hepatitis A is spread when someone ingests the virus through close contact with an infected person or by having contaminated food or drinks. Symptoms include inflammation of the liver, fever, low appetite, nausea, vomiting, diarrhea, muscle aches, and yellowing in the whites of the eyes and the skin (jaundice).

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