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Think Again Before You Slurp Down That Oyster

Posted in Outbreaks & Recalls,Vibrio on July 12, 2018

Raw oysters are often linked to vibrio illnesses. As ocean temperatures rise, the cases of vibrio linked to raw oysters has risen as well.

But raw oysters tend to be paired with another concerning pathogen, norovirus. And we see this link more often than one would think.

Norovirus Outbreak 2018 Linked to Oysters

In April of 2018, the United States and Canada investigated the causes of an outbreak of norovirus that sickened hundreds of people across multiple Canadian provinces and American states. Investigators believed that the norovirus was spread by raw oysters harvested from south and central Baynes Sound on the Pacific coast of the western Canadian province of British Columbia.

A statement from the California Department of Public Health said that approximately 100 people had reported signs of illness after eating oysters from British Columbia that they bought at various restaurants and seafood distributors located throughout the state. The director of the CDPH recommended that Californians avoid exposure to raw and undercooked shellfish.

Canada’s public health authorities opted to temporarily close the Baynes Sound fisheries, according to a statement put out by Canada’s federal government. They announced that more than a hundred people in British Columbia had been sickened by late April, with more than a dozen cases in Alberta and Ontario as well. They also recommended that consumers exercise prudence when consuming shellfish and cook oysters to a sufficient internal temperature before eating.

The American Food and Drug Administration released a statement on their website with much of the same information. They did say, however, that the outbreak of norovirus in the United States wasn’t limited to California; cases had been reported in the states of Alaska, Illinois, Maryland, New York, and Washington as well.

According to the website Chek News, British Columbia’s oyster harvesting industry has taken a financial hit in the wake of the norovirus outbreak. Several fisheries closed voluntarily while Canadian authorities investigated the source of the outbreak. Other shellfish farms that opted to stay open nonetheless experienced a serious reduction in revenue; a representative of an industry group who spoke to CHEK estimated that sales had dipped by 50% in the wake of the outbreak.

But We Have Seen This Before; Norovirus in the News

This outbreak isn’t the first time that Canada has seen a wave of norovirus cases linked to shellfish. The industry weathered a similar event last year – 400 people got sick over the course of about five months, according to an article published by CBC News. As a result, the shellfish industry in British Columbia experienced losses to the tune of 9.1 million Canadian dollars.

No specific cause came out of the investigation of that 2017 outbreak. This time around, public health officials are hoping to pin down the cause of this year’s wave of norovirus and in doing so help to reduce the possibility of future outbreaks.

The BC Shellfish Growers Association indicated to CBC News that they suspect pollution is part of the problem; illegal dumping of sewage from vessels, poor septic systems and unsanitary practices were all cited by a spokesman as potential sources of the outbreak. An epidemiologist with the Centre for Disease Control said that norovirus typically finds it way into shellfish like oysters when they’re exposed to water contaminated by human sewage. Because shellfish are filter feeders, they get their food by straining ocean water to “filter out” tiny particles that they can eat. If there’s norovirus in the water, shellfish can suck it in while trying to feed, thus introducing it into their bodies.

According to the Washington State Department of Health, norovirus reaches shellfish via untreated human sewage or vomit. They recommended that homeowners take care to make sure that their septic systems are properly maintained, and that beachgoers avoid vomiting or pooping on the beach. Additionally, boat owners should avoid vomiting or pooping off of their boats; WSDH recommends that they empty their boat’s septic tanks at an appropriate pump-out station.

Looking Out for Norovirus

The sickness caused by norovirus is not unlike the flu. Affected individuals usually experience nausea, painful stomach cramps, vomiting, and diarrhea. Norovirus isn’t usually deadly, although it does sometimes kill – the elderly, children under five, and immunocompromised individuals are at the highest risk of serious illness or death from norovirus.

Oysters contaminated with norovirus do not display outward signs of danger – most of the time, they will look, smell, feel and taste like non-contaminated oysters. Just like oysters contaminated with vibrio bacteria. Norovirus is highly contagious and can survive on surfaces and in containers that have been used to transport or prepare oysters. It’s a fast-acting pathogen, with symptoms usually presenting within 12 to 48 hours of exposure. They typically last from one to three days.

Norovirus can survive for long periods of time in cold water, so there’s often an uptick in cases during the winter months between November and March. It can survive for weeks on hard surfaces, and in water may be able to survive for months or years. Got that? More likely to get norovirus in the winter and vibrio in the warmer months from raw oysters.

There’s no vaccine for norovirus yet, and according to the CDC it’s responsible for fully half of the outbreaks of foodborne disease in the United States. Worldwide, it’s estimated to cause one out of five cases of gastroenteritis. The best way to guard against the disease is to disinfect surfaces with hot water and soap. Alcohol-based disinfectants are not as effective at eliminating the virus. Shellfish should be cooked to an internal temperature of 145 degrees Celsius; extra precaution should be taken with oysters, which are often consumed raw.

Several different public health agencies at the state and federal level in the United States and Canada offer up-to-date information about fishery closures, warnings, and proper precautions to avoid norovirus.

So, before you shuck and swallow that raw oyster, it may be a good idea to think twice and cook it. Maybe broil it? Eat it blackened? Boiled? Or even fried.


By: Sean McNulty, Contributing Writer (Non-Lawyer)