British Columbians are being warned after dozens of recent cases of acute gastrointestinal illness have been linked to oysters, according to the B.C. Centre for Disease Control.

The organization that tracks disease outbreaks in the province said more than 70 cases of oyster-related illness have been reported in several health authority regions since early December, including Vancouver Coastal Health, Fraser Health, Island Health and the First Nations Health Authority.

For fans of raw oysters and restaurants specializing in oysters, that's bad news.

"We're probably going to take some lumps. If I had to guess, it's definitely going to be a bit of a slower evening for us," said Doug Stephen, owner of Merchant's Oyster Bar on Friday.

"We'll take a bit of a downturn for about a week. I really hope that doesn't happen though."

"It's a scenario that's usually outside the control of what we can do on the restaurant level, but more importantly, we've really focused on working with a producer that does the utmost of due diligence," said Stephen.

"There are some suppliers that basically ship into large warehouses where they're going to be sitting in salt water tanks. The potential for cross contamination is huge," he said.

Outbreak likely to continue for weeks

The BCCDC expects the outbreak to last several more weeks and dozens more people are likely to get sick.

"What we're seeing now is a widespread problem over the course a few weeks," said Dr. Eleni Galanis, epidemiologist at the BCCDC.

"We have seen oyster-related outbreaks with norovirus in the past, but this is one of the biggest ones and also one of the longest ones we've seen in a long time."

"The majority [of people affected] have vomiting and diarrhea, very frequent, multiple times a day for two to three days," she said.

"It's very unpleasant, I mean, basically you can't go to work. You can't go to school and you have to stay at home to be close to the bathroom."

'Cook oysters thoroughly'

People affected by the outbreak reported eating raw or lightly-cooked oysters at home and in restaurants, according to the BCCDC. None of the cases involved canned products.

Galanis said that the BCCDC is working with the relevant health authorities to investigate, as well as with the Canadian Food Inspection Agency, Fisheries and Oceans Canada and Environment Canada.

"We haven't found the smoking gun. How did the norovirus get into the oysters in the first place? We know that oysters are filter feeders so they can become contaminated with any microorganism that's found in ocean water or any microorganism that infects someone who handles those oysters," said Galanis, adding that the virus is generally transmitted through human sewage or fecal material.

"In order to kill norovirus and other bugs, people need to cook oysters thoroughly to an internal temperature of 90 C for 90 seconds," said Galanis, adding that lightly pan frying oysters isn't enough to eliminate norovirus.

She says the only good news about norovirus is that it usually resolves itself without medical intervention.

Anyone who becomes ill with diarrhea and vomiting after eating shellfish is asked to call BC HealthLink at 811.

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