Public health agencies are warning of a outbreak of food-related illness that is believed to be connected to raw oysters imported from British Columbia.

Since March 12, Public Health – Seattle & King County has reported over 40 different cases of food-borne illness all believed to be tied to the consumption of raw oysters. With Seattle restaurants being responsible for the bulk of the suspected oyster-illness cases, the department also reported cases in Federal Way, Issaquah, Kirkland and Woodinville.

Norovirus, which according to health officials can often be transmitted through raw oysters, is believed to be the illness in all the reported King County cases.

During the first week of April, both the Washington Department of Health and the U.S. Centers for Disease Control and Prevention issued public alerts after identifying norovirus outbreaks that were suspected to have originated from oysters imported from the South and Central parts of Baynes Sound in British Columbia, Canada.

As of April 6, at least 103 norovirus illnesses have been reported from 13 states including California, Colorado, Florida, Hawaii, Illinois, Massachusetts, Minnesota, New Jersey, Nevada, New York, Oregon, and Texas. Washington has the most cases reported of any state with 62, followed by California with 34 cases.

On April 8, health officials in Canada reported 293 cases of illness related to the consumption of raw oyster since the beginning of the year.

The U.S. Food and Drug Administration advised restaurants and retailers not to serve or sell potentially contaminated raw oysters from Canada.

Food safety attorney Bill Marler, said that shellfish are filter feeders so when Norovirus enters the water through sewage and vomit from leaky septic systems, faulty wastewater treatment plants, boaters, or beach-goers, oysters can take the virus into their bodies.

According to the Washington Dept. of Health, symptoms of Norovirus infection may include vomiting and diarrhea, nausea, muscle aches, fever, and headache. Symptoms typically start 12 to 48 hours after consumption of contaminated food and last for one to three days. Most people recover without treatment.