The B.C. Centre for Disease Control says four shellfish farms have been closed after being linked to the outbreak of noroviruses associated with raw B.C. oysters.

As of April 26 the outbreak includes 132 cases of illness in B.C., a decrease from last week, according to a release.

An investigation by the BCCDC found that most people were infected after consuming oysters harvested in south and central Baynes Sound.

The investigation into the sources of contamination is ongoing.

British Columbians were first warned after dozens of cases of acute gastrointestinal illness were linked to oysters in January 2017.

In February, the outbreak became the subject of a federal investigation.