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Norovirus on the half shell: B.C. flummoxed by raw oyster contamination

Workers harvest B.C. oysters in 2015 at Sawmill Bay Shellfish on Read Island. The company is owned by Steve Pocock, who has voluntarily halted harvesting at his farms since January due to fears generated by a norovirus outbreak.

John Lehmann/The Globe and Mail

It was well after midnight by the time the gala began to wind down. The last of the attendees gathered their coats, stuffed after hours of indulging at the oyster-themed party – countless oysters served straight off the barbecue and raw on the half-shell.

The mid-November event capped off the Clayoquot Oyster Festival in Tofino, B.C., which every year celebrates the launch of oyster harvest season in the small coastal town. Over the course of that November weekend, more than 500 people slurped back more than 11,000 glistening B.C. oysters.

In the eyes of the organizers on that night, the weekend had been a success. "We all looked at each other and said, 'This is the easiest event we've ever done,'" said Bobby Lax, the festival's co-ordinator.

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But by the next day, Mr. Lax would watch with growing horror as a crisis unfolded.

First, just one illness was reported. Then, dozens. All of them had similar symptoms, including vomiting, diarrhea and abdominal pain. Soon, health officials declared that 118 people were suffering from norovirus – most of them festival guests.

Local officials initially considered it an isolated incident. But the crisis was just beginning. The festival in Tofino would soon plunge officials at all levels of government, from Vancouver Island to Ottawa, into a mystery that continues to elude them five months later.

Over that time, health officials would hear of hundreds more incidents linked to oysters from up and down the B.C. coasts. From December on, an additional 321 cases were reported to the Public Health Agency of Canada (PHAC) – in B.C., Alberta and Ontario – with some cases requiring hospital visits for dehydration.

By scale and size, officials are calling it the worst norovirus outbreak related to oysters in B.C. history. Still, epidemiologists and public health officials remain flummoxed as to the cause of the contamination. And with every day the outbreak drags on, the anxiety worsens for the shellfish farmers who produce about 60 per cent of Canada's oysters, an industry with annual sales of $11.7-million.

Investigating oyster-borne illnesses is almost always a tricky business. Those who enjoy oysters often enjoy them by the platter, with each one containing several varieties from several locations. Even a single case of illness can be complex, let alone hundreds. But other unusual factors have made this case even more complicated.

"It's been a frustrating and difficult and prolonged investigation," said Eleni Galanis, an epidemiologist at the BC Centre for Disease Control who is co-ordinating the investigation at the provincial level.

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Most confounding has been scale, both in terms of geography and the length of time the outbreak has endured.

In a typical situation, after multiple illnesses are reported, authorities work backward to identify a common restaurant or retailer. From there, they gather information on where the oysters were harvested. In the most straightforward cases, multiple reports of illness will link to a single farm.

But in this case, contaminated oysters have come from multiple farms and areas, including many locations separated by hundreds of kilometres – the east and west coasts of Vancouver Island, and along the main B.C. coast.

To date, seven oyster farms have been shut down after tests indicated norovirus was present or suspected. The province has about 460 shellfish farms, not all of them active.

Still, Dr. Galanis believes the cause of contamination is likely a single source. "It could be multiple sources – multiple local sources of human sewage in each of those areas that have been contaminated," she said. "But it's hard to believe that contamination could happen in multiple areas at the same time."

In medicine, she said, "when a patient comes with a variety of different symptoms that don't seem to be related or seem to be multiple things, we learn that the most likely explanation is a single problem."

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At this point, human sewage is her best guess. Among the theories officials are considering is the possibility of nearby municipalities or boaters dumping sewage into the waters. Norovirus is typically transmitted through person-to-person contact or through fecal contamination in water or food. Oysters are filter feeders and, in the process of filtering food out of the water, can become contaminated. Norovirus can live in the oyster for 10 weeks.

After the Tofino incident in November, reports of illness slowed, then picked up against around Christmas. In the second week of January, the PHAC received more than 60 reports.

At first, Dr. Galanis said, some officials did not believe the illnesses could be related. But one long-time member of her team brought up a similar case in B.C. from 2004, in which dozens of norovirus illnesses were traced to 14 separate sites.

The cause of contamination in that 2004 case was never identified, and authorities worry the same could be true this time.

"To understand what has happened here as well as we possibly can, we need to identify that source of contamination," said April Hexemer, the manager of outbreak management division at PHAC. "… It's not stable, the water's always moving, so it makes it a challenge."

In recent weeks, the number of reported illnesses has tapered off again, raising hopes that the outbreak is at its last gasp. But Ms. Hexemer said those figures are likely to be updated soon with additional cases. She said it is not likely the outbreak will be declared over for at least a few more weeks.

This will be unwelcome news for Steve Pocock, an oyster farmer on Read Island, just north of the Georgia Strait.

Since late December, he has had "virtually zero" oyster sales. Even though his farm tested negative for norovirus, he voluntarily stopped harvesting in January just to be safe. He had to lay off three employees and reduce hours for his remaining staff.

His processing plant, usually a hive of activity where he sells 3,000 to 4,000 dozen oysters each week, has been closed entirely. And it is too soon to tell whether he will be able to recoup his losses. He worries that as soon as the outbreak is over, the market will be flooded.

"It's a bit like selling apples – people wouldn't eat twice as many apples after a shutdown," he said.

This recent outbreak comes on the heels of a case in 2015, when dozens fell ill, also after eating B.C. oysters, in an outbreak of vibrio parahaemolyticus, which is caused by increased water temperatures.

"The farmers are the innocent bystanders in this," Mr. Pocock said. Despite their best efforts to ensure safety, he said, some factors are out of their control.

Mr. Lax, the festival organizer in Tofino, echoed this sentiment. "It's been absolutely heartbreaking for us to watch what's been going on," he said. He added that he and other organizers recognize the seriousness of the illnesses. But he also emphasized the pleasure of eating oysters – a food he feels passionate about.

"The best thing I heard from those who got sick is, 'Yes, I got sick, it sucked, and I will see you next year," he said. "An oyster lover is willing to take the chance."

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