Noroviruses are part of a group of viruses understood to be the most common cause of stomach upset. They cause nausea, vomiting and diarrhea, and people may also have a fever and head and muscle pains.
Although an individual’s symptoms may pass in one or two days, the disease is highly contagious and remains in the faeces for several weeks afterwards.
Finland was hit by outbreaks of the bug in May and June, and analysis confirmed that Polish raspberries were the cause. The fruits are now suspected as having caused the new cases have been reported in the south since the beginning of this month.
Evira has not said now many people are currently known to have become sick, but they are thought to have been infected after eating desserts and cakes made with frozen raspberries that have not been heated before use. The virus can enter the fruit through contaminated irrigation water, and it stays alive and contagious during freezing.
In order to safeguard against infection, users of foreign frozen raspberries should heat the fruit to 90 ºC for at least two minutes, says Evira. Slight heating after defrosting is mot enough to ensure the raspberries are safe.
“Heating is also recommended for other frozen berries of foreign origin, if they are served to persons in risk groups, such as elderly people, children or persons with impaired resistance,” it says.
Although a suspected lot of raspberries has been withdrawn from the market in Finland, it is still advisable to check the country of origin for frozen raspeberries. This must be indicated on the pack, even if the fruit are packed in Finland or a third country.
The Finnish outbreaks are not the first time raspberries have been implicated in making people sick.
A large batch of frozen strawberries imported from Poland to Denmark in 2005 was found to be carrying the norovirus after over 1000 people who ate them became sick.