The British Columbia Centre for Disease Control is warning consumers to take steps to protect their health after two B.C. Vancouver Island oyster farms have been closed following an outbreak of norovirus associated with eating the raw shellfish.

The B.C. Centre for Disease Control says about 40 cases of acute gastrointestinal illness have been connected to eating raw oysters since March. All of the ill people reported eating raw B.C. oysters. Testing has confirmed some of the cases were norovirus.

In late 2016 and early 2017, more than 400 norovirus outbreak cases associated with raw or undercooked B.C. oysters were reported in B.C., Alberta and Ontario, according to the Centre for Disease Control.

Federal officials with Fisheries and Oceans Canada confirmed the farms affected now are on the east coast of Vancouver Island at Deep Bay and Denman Island.

The two farms are no longer harvesting oysters, but no recall of oysters has been issued by the Canadian Food Inspection Agency.

The precise sources of contamination have not been identified, but human sewage in the marine environment is believed to be the most plausible cause of shellfish contamination, according to Centre for Disease Control epidemiologist Marsha Taylor.

In late 2016 and early 2017, norovirus cases associated with raw or undercooked B.C. oysters led to the closure of 13 farms. Human sewage was suspected as the cause then, as well.

Norovirus is a highly contagious cause of gastroenteritis and can be spread by contaminated foods, beverages, countertops and other hard surfaces, and person-to-person.

Anyone who falls ill with diarrhea and vomiting after eating shellfish should call B.C. Healthlink at 811, said Taylor. Most people recover from norovirus on their own with proper hydration and rest, but in some cases dehydration can be severe and require hospitalization. Consumers should also report oyster-related illnesses to their local health authority for investigation and follow-up.

In order to kill norovirus and other pathogens, the British Columbia Centre for Disease Control recommends consumers cook oysters thoroughly to an internal temperature of 90 C for 90 seconds. The bottom line is: Officials discourage eating raw oysters.