Since December, 56 cases of Hepatitis A have been reported in Sweden, more than ten times the normal number of cases for the same time period, the Svenska Dagbladet (SvD) newspaper.
While eight of the Swedish cases have been confirmed to be the same strain from a similar outbreak in Denmark, Danish health officials believe an additional 12 Swedish cases are also likely linked to the same strain of Hepatitis A that is thought to have originated in frozen berries.
"We think the source is a large batch of frozen berries from one producer that has spread across the Nordic region," Swedish National Food Agency (Livsmedelsverket) spokesman Mats Lindblad told the TT news agency.
He said it was difficult, however, to pinpoint disease-carrying batches.
"It's like finding a needle in a haystack, because there only needs to be a very small amount of the virus for it to spread."
Last week, the agency warned Swedes that they should make sure they cook berries they buy frozen in the supermarket to make sure there is no risk of infection.
Denmark and Finland had both already warned their consumers of the risk and asked that people take precautions in how they eat store-bought berries. Already in 2009, Finnish authorities asked that consumers make sure to boil raspberries. Denmark legislated back in 2001 that cafés and restaurants had to do the same if the raspberries were imported.
Experts with the Swedish Institute for Communicable Disease Control (Smittskyddsinstitutet, SMI) 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 Swedish Communicable Disease Institute, told the TT news agency at the time.
"This cooking advice applies to all kinds of frozen berries from all suppliers. This is the safest option until we find out more."
On Tuesday, the agency announced that ten cases of Hepatitis A have been linked to the strain in the Danish outbreak, with an additional seven cases suspected of being linked.
Tests runs by the agency indicate that there is no evidence that Swedish consumers should shy away from any particular kind of berry. Hepatitis A can lead to liver damage.
The most recent case in Sweden was reported on April 6th.