The Swedish Institute for Communicable Disease Control (Smittskyddsinstitutet, SMI) warned that the berries may have been responsible for 22 cases of Hepatitis A in Sweden so far.
The usual contagion rate for the same timeframe is about five people in Sweden.
Experts from the institute advised berry lovers to take caution when consuming any berries bought in Sweden that were sold frozen.
“If you cook them for at least one minute then all the contagion will die or disappear,” Margareta Löfdahl, epidemiologist from the Institute, told the TT news agency.
“This cooking advice applies to all kinds of frozen berried from all suppliers, this is the safest option until we find out more.”
The people infected in Sweden were infected with the same type of Hepatitis that 30 people in Denmark were diagnosed with recently, which has since been traced to frozen berries and strawberries in particular.
The SMI is now sending traces of the berries to the Swedish National Food Agency (Livsmedelsverket) for testing.
Hepatitis A is an infection of the liver. It can be prevented by vaccination, and experts at SMI have recommended Swedes remember to maintain good hygiene.