Investigators search for culprit behind norovirus outbreak in B.C. oysters

Shawn Chesney smiles as he deftly pries opens a craggy oyster shell with a stubby knife and frees the glistening meat inside. Shellfish isn't just an appetizer at Oyster Express, his Vancouver restaurant. 

"Oysters really do transcend class. They transcend race. They transcend age," Chesney said. "Nutritionally, they're great for you. There's obviously a romantic aspect to it." 

But that romance comes with risk when an oyster's draw is eating it raw. Between January and April more than four hundred people in the U.S. and Canada became ill with norovirus traced back to raw shellfish from oyster farms in Baynes Sound. 

The narrow, 40 kilometre channel between Vancouver Island and Denman Island is B.C.'s most prolific oyster farming region. 

Recalls affecting industry's reputation

Norovirus causes stomach cramps, nausea and diarrhea. The pathogen that makes people sick is spread through human feces and vomit. Cooking oysters at 90 C for 90 seconds kills the virus. It can also kill business. 

"Even though people do love oysters, they will take a break or they'll stay away," Chesney said, reflecting on how several months of recalls and food safety warnings affected his restaurant until the outbreak was declared over at the end of April.

The damage to the B.C. brand was much greater, according to Nico Prins, the executive director of the B.C. Shellfish Growers Association. 

"I think it's got a huge reputational impact on the entire B.C. industry as a whole," Prins said of international headlines and recall notices that buried details of the problem in fine print: the contamination was traced to just 14 out of more than 500 growing sites.

The Department of Fisheries and Oceans shut down the affected sites under the direction of the Canadian Food Inspection Agency.

Prins said the publicity from the recalls is something that "sits with the importers and the food safety officials of other governments and other countries for much longer than it would with the consumer."

The outbreak frustrated an expected recovery after oyster sales plummeted during the pandemic. The most recent figures from B.C.'s Ministry of Agriculture and Food peg provincial oyster sales at just under $20 million in 2020, down from more than $28 million the year before. 

Although his shellfish business, Mac's Oysters, is based in the heart of Baynes Sound, general manager Gordy McLellan says none of the 250 hectares he leases from the B.C. government were touched by the norovirus taint. He says his competitors didn't fare as well. 

"There's a couple of guys that are pretty upset about it because they didn't get any sicknesses and their orders went way down."

Detecting norovirus

Like all producers, McLellan is subject to regular and routine scrutiny under the Canadian Shellfish Sanitation Program (CSSP), which is administered by no less than three federal government departments: Environment and Climate Change Canada (ECCC), Fisheries and Oceans Canada (DFO) and the Canadian Food Inspection Agency (CFIA).

McLellan says if one of his sites goes a week without a water quality test during the summer, alarm bells go off in government offices and the site is closed. 

"Keep your head down and try to not get anybody sick," he said with a smile that belies the burden of work involved in preventing illness.

Oysters aren't tested for norovirus before they're shipped. That's partly because the test results would take too long for a product with limited shelf life. Norovirus can also be difficult to detect. While a gram of human waste about the size of a quarter of a teaspoon can contain up to 10 billion norovirus particles, it takes as few as 10 particles to cause illness.

But testing the oysters themselves for norovirus isn't practical. Conclusive results for the presence of viable virus can take weeks. So producers work with ECCC to look for E. coli in the water where the oysters are grown which can reveal exposure to sewage. But a finding of low or zero levels of E. coli doesn't mean there isn't norovirus clinging to the oyster. In addition, producers are responsible for testing for a variety of toxins such as paralytic shellfish poisoning (PSP). 

Every bag of oysters shipped to market must have a tag attached describing the location and date the shellfish were harvested, so they can be traced back to the exact beaches or growing sites in the event of an outbreak. Retailers and restaurants have to retain the tag for 90 days in case of a reported illness and subsequent investigation.

Contamination events like this recent one are becoming more frequent, according to Lorraine McIntyre, a food safety specialist at the B.C. Centres for Disease Control (BCCDC).

"We've had outbreaks in 2015, 2016, 2017, 2018," McIntyre said. "We had a little break with COVID. And now here we are in 2022." 

Sewage dumping suspected cause of outbreak

When the BCCDC investigated the last event, it pointed the finger at commercial fishing boats that were anchored within metres of some farms. 

Transport Canada regulations forbid dumping untreated sewage within three nautical miles (5.5 km) of shore. Boats without onboard sewage treatment are supposed to use marina-based pump-out stations. 

The BCCDC says station operators contacted for its investigation said commercial vessels rarely if ever used them. There are no regulations requiring vessels or stations to keep records. Most vessel owners refused to answer the BCCDC's questions, though one did admit that dumping sewage was a common occurrence. 

"Well, it's difficult," McIntyre said of getting 100 per cent compliance with existing regulations for disposing of sewage. "Education only works for people that listen." 

Transport Canada can enforce the dumping regulations with everything from verbal warnings to summary convictions. However, a spokesperson told CBC News the department hasn't recorded any fishing vessel violations since 2018, but did find what it calls "deficiencies" in sewage treatment systems or holding tanks on 50 vessels of all types over 15 gross tons in the past three years. The spokesperson said that prosecutions would require DNA collected from the discharge to trace it back to an offender.

The department has produced pamphlets encouraging all vessel operators to follow the law. Every two years Transport Canada conducts targeted inspections of fishing vessels. Last year, that amounted to 101 vessels nationally. 

Last year the U.S. Coast Guard (USCG) boarded or inspected 3,323 vessels checking for sewage discharge compliance in American waters right next door to some of B.C.'s oyster farms, according to the chief of the USCG's Inspections Division for Puget Sound. Commander Lee Bacon told CBC news the Coast Guard issued three citations for noncompliance.

Robert Morely, a spokesperson for the commercial herring fleet, balks at the blame being heaped on fishing vessels, telling CBC News in an email that there are recreational and live-aboard vessels in the area year-round.

He also said other potential sources of the outbreak include "sewer overflows, wastewater treatment plants and municipal raw sewage discharge and overflow from local septic systems." 

Residential developments and industrial operations are encroaching on Baynes Sound, a sensitive body of water on which shellfish producers rely. 

Just a short drive from Mac's Oysters the growing village of Cumberland discharges treated waste water into Baynes Sound via the Trent River. Union Bay Estates, which is still under development, envisions nearly three thousand homes in a development right on the shore, next door to a ship-breaking operation being sued by the Comox Valley Regional District. 

"It's possible that there's been septic seepage. It's possible there's been a commercial vessel discharge, but that doesn't explain everything," McIntyre said of this year's outbreak which is still under investigation. The only thing certain about the contamination is that it's caused by people.