The test results showed that norovirus, which causes winter vomiting disease, was the cause, but more tests were needed to determine the virus's origin.
It is now clear that the virus came from unopened packages of nori sheets, which are used to roll sushi, Göteborgs-Posten reports.
"Now we are raising the alarm about this in the food chain in Sweden," says Anna Engström, head of the environmental unit in Lerum municipality, to GP.
