Food poisoning – don't blame it on the oysters

27 November 2009 by
Food poisoning – don't blame it on the oysters

They're often blamed for food-poisoning outbreaks, and many people are wary of eating them. But do oysters really deserve their bad press? Tom Vaughan investigates.

Eight years ago seafood chef Mitch Tonks had a run-in with an oyster. What exactly was to blame he has never established. "I had a dozen oysters and shortly after started to go into anaphylactic shock," he says. "I rushed to the hospital and the doctor told me I'd developed an allergy to oysters, and maybe to all shellfish. Obviously that could have been a disaster for me professionally. Plus I love oysters."

Keen to ensure this diagnosis was 100% correct, Tonks picked up half a dozen oysters a day or so later, drove with his wife to the hospital, pulled up in the car park and shot back all six. "I knew that if I went into anaphylactic shock again, the hospital was just across the threshold," he says. He sat and waited, but after an hour or so symptom-free, the couple drove home, and he has continued to enjoy oysters on an almost daily basis.

Ever since people started eating raw oysters, there has been an associated wariness. Most of us know of someone who has had a bad oyster. And we all know the risks of turning up a bad one ourselves. But of late, oysters have been at the sharp end of a particularly acute drubbing.


Earlier this year, a Health Protection Agency (HPA) report into the mysterious bug that saw 500 customers at Heston Blumenthal's Fat Duck restaurant fall ill pinpointed raw oysters as the culprit, saying the incident "confirms the well-known risks that raw shellfish pose". Then the national press picked up on the fact that a diner who passed away shortly after visiting D&D London's Quaglino's restaurant had eaten oysters for the first time there. Then, just as it was shaping up as a pretty bad year already for the little molluscs and their producers, the Food and Drug Administration in America announced that Gulf Coast oysters harvested during warm weather - that are not treated with anti-bacteria technology - are to be banned from 2011, owing to the prevalence of Vibrio vulnificus, a bacteria supposedly to blame for the average 15 oyster-related deaths in the USA each year. Suddenly, we've put a magnifying glass to the minute risk of raw oysters. Why, exactly, is not really clear.

Let's put things in perspective: Tom Pickerell, director of the Shellfish Association, says that last year, more people got ill from eating unpasteurised cheese than oysters. "It is just one of these things that the public have concerns about," he says. "Our regulations are some of the strictest in the world."

Britain produces almost 14,000 tonnes of oysters - Pacific and native - per year. In the past 12 months, there were only four incidents of food poisoning outbreaks related to shellfish, one of which was at the Fat Duck. A fraction of the illness caused by, say, barbecues.

Yet there are nonetheless some risks associated with oysters. The danger comes principally from their filtration system. Unlike crustacean shellfish such as crabs, shrimp and lobster, molluscan shellfish obtain nutrients by pumping seawater through their gills and filtering out tiny organisms, which are then ingested. While pumping water, they can take in bacteria, viruses and chemicals, concentrating them in their bodies at much higher levels than found in the surrounding waters. If not cooked and the contaminants not killed or neutralised, they can then make people very sick indeed.

Rex Features
Rex Features

However, the testing and purification processes oysters go through makes the possibility of a dangerous one arriving on your plate very small indeed. At oyster producer Loch Fyne, for example, tests are rigorous. "When you are dealing with a large batch of oysters you have to have reassurance," says production director David Attwood. "We never assume that a site with a good history will always have a good history. There could always be some contamination."

Legislation insists that all oysters are screened for E coli and salmonella, and producers also regularly check for norovirus. Oysters are also then purified, where they are held in tanks of seawater that is continuously pumped through an ultraviolet chamber; a process that works very well at destroying bacteria, which are flushed from the mollusc's gut into the chamber to be killed. The chances, after all of this, of the oyster harbouring noxious contaminants are, according to some experts, very slim indeed.

Nonetheless, these are risks that some aren't prepared to take. Michael Caines, who heads up the kitchen at Michelin-starred properties Gidleigh Park and the Bath Priory, as well as overseeing signature restaurants at four Abode Hotels, removed oysters from his menus this summer. "It's not worth the risk of upsetting a wonderful evening for a diner at one of our properties," he says. "Not just because of the toxins in the oysters, but because people can be very allergic to them. If someone is sick it's very possible you might have to compensate them and oysters are just one luxury ingredient out of countless others."

The NHS states on its website that, according to the Food Standards Agency (FSA), there are about 850,000 cases of food poisoning each year in the UK and about 500 deaths from it. If you cast your mind back over the past 12 to 18 months, the only two single-case food poisoning deaths reported in the national press were the death of a forager last autumn from mushroom-poisoning and the alleged oyster incident in D&D London's Quaglino's in May. As it happens, both Quaglino's and its oysters were cleared of any involvement in the woman's death, a fact not widely reported, which goes to strengthen the Attwood's argument, that "people will always look to blame an oyster".

Pickerell agrees: "When people have a three-course dinner, some wine and then fall ill it's always put down to the shellfish. Their danger is blown completely out of proportion."


Likewise, the Fat Duck case is not all black and white - at least not according to the shellfish's supplier, Colchester Oyster Fisheries. "There is no concrete proof that our oysters were responsible for the outbreak," says the company's operations manager, Graham Larkin. "The only link is one of our beds had traces of norovirus on it, described by the environmental health officer as low to moderate. The highest count of the virus per gram of meat was 42; the FSA level of acceptability, before the body starts to struggle to kill it off, is anything up to 100. It probably wouldn't have harmed anyone anyway. It happened in January and February when winter vomiting disease is quite common."

The HPA report found that the scale of the outbreak was also exacerbated, by a slow response time from the restaurant and from staff returning to work too soon after falling ill.

Larkin blames the water companies for the original contamination, as human excrement was the most likely cause of any norovirus present in the oyster. While the Environment Agency claims that, over the past 10 years there has been a steady but gradual and sustained improvement in shellfish waters, with pollution reduction plans bespoke to each site, Pickerell questions where they find their proof.

"Ten years ago we had 40% of our shellfish waters classified as grade A (see page 30). Now there are no grade A waters in the UK," he says. This, however, sounds worse than it is. The Government's objective to get sites up to class B has been very successful, and an oyster from a class B site that has undergone depuration is, Pickerell insists, actually safer than one from a class A site, which are deemed fit for immediate consumption. The wide-scale downgrading has no effect on the safety of the oyster; the problems arise with the added cost of depuration burdened on the shellfish industry.

The checks and regulations placed on oysters are tougher than ever and the improvement in technology to test for virus and bacteria is reflected in the low number of shellfish-related food poisoning outbreaks. So why the sudden focus on oysters as dangerous? Tonks and Larkin both see it as a symptom of the nanny-state, policing rigorously what we eat. Opinion towards the Gulf Coast raw oyster ban in the USA is similar. "They're eliminating the choice from consumers by saying, ‘You're not smart enough to make your own decisions,'" said Tommy Cvitanovich, the owner of Drago's restaurant in Metairie, Louisiana, when speaking to the New York Times. Salmonella causes 30 times more deaths across the USA each year than the Vibrio vulnificus bacteria in Gulf Coast oysters, but shellfish are far easier to pinpoint and police.

Certainly there is absolutely no evidence there is any more risk in eating an oyster than there has ever been. It's just we are naturally wary of raw food, Tonks says, and the smallest coverage of oyster-related sickness in the press is likely to start a bandwagon effect. So it doesn't help that it was the Fat Duck - one of Britain's pre-eminent restaurants and a household name - that suffered the outbreak. Had it been a village pub, oysters would have taken up far fewer column inches this year.

It'll be interesting to see whether, should the proposed ban in the USA come into effect, a stricter regulation of oysters takes hold in other countries. But with any luck, 2009 will simply be the oyster industry's annus horribilis, with the Fat Duck incident, in Tonks's words "just one of those things that happens". And, like Tonks in that hospital car park, we can just hope that things go back to normal.


  • The UK produces 13,000 tonnes of Pacific oysters and 600 tonnes of native oysters annually from its 124 designated shellfish waters. By comparison, France produces 130,000 tonnes, second only to China for the scale of its production, and the average Frenchman eats 50 oysters a year.
  • The UK's oyster industry is worth £30m a year, an increase of £5m from two years ago. Continued growth is also apparent, with Colchester Oyster Fisheries reporting a sales increase of 30% over the past year.
  • Shellfish waters are graded with regards to their safety for consumption. Shellfish from an A-grade site are fit for immediate human consumption. B-grade shellfish require 42 hours of depuration. C means the shellfish must be relaid in cleaner waters and purged of impurities, and D means the beds must be closed until things improve.
  • A herpes virus in French oysters is in danger of sending its industry into crisis. Producers are reporting the loss of between 40% and 100% of one-year-old oysters. The disease has appeared briefly in the Channel Islands but has not spread and as yet has not appeared on any other oyster beds in the UK.
  • The Romans popularised oysters in Britain, with large numbers of shells having been found at Roman sites. Through to Victorian times, oysters occurred naturally in such large numbers that they were seen as a food for the poor. In Charles Dickens's The Pickwick Papers, Sam Weller remarks: "Oysters and poverty always seem to go together."
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