In Denmark authorities are almost certain that berries are behind the around 30 cases of infection there. No other common cause has been detected.
An unusual number of hepatitis A cases have also been reported in Norway and Finland.
Hepatitis A spreads through a virus which can survive freezing temperatures. Sweden's National Food Agency recommends boiling frozen berries for one minute to kill the virus. The berries can then be frozen again.
"We cannot say with absolute certainty that frozen berries are behind this but it is very likely since we have found the exact same virus stock among patients here in Sweden and in Denmark where a very careful investigation has been carried out and they have found no other explanation," said Margareta Löfdahl of the Swedish Institute for Communicable Disease Control.
Sweden's National Food Agency is currently conducting its own analysis.