Danish authorities are again recommending frozen raspberries be rapidly boiled before being used in smoothies, desserts and other dishes. The fruit must cook one minute.

Outbreaks of norovirus have stricken hospital staff, canteen and restaurant guests and individuals who have been eating frozen raspberries from abroad.

"Food Administration takes this situation very seriously, and that is why we now recommend the boiling of frozen raspberries both at home and businesses such as restaurants and cafeterias," says Annette Perge in the Food Agency.