Norovirus is the most common stomach bug in the United Kingdom, affecting as many as 1 million Brits per year. Unfortunately, thanks to the broader U.K. media it’s a virus that is also heavily and unfairly associated with eating oysters.
In truth, it’s a link that has been taken out of all context: there wasn’t one single proven illness from norovirus or any other virus to do with shellfish in 2012, while last year there were four outbreaks associated with oysters. Although those four outbreaks were not proven, tests showed the shellfish were the likely cause. There was, for example, a norovirus outbreak at Oxford University in 2013 that affected a few hundred people and oysters got the blame, but it was also found that about 20 percent of the people that were taken ill didn’t eat the oysters.
Despite such low figures, the country's Food Standards Agency (FSA) has issued a new call for proposals to design and execute a research study that will identify and evaluate possible enhancements to norovirus removal from live oysters during shellfish depuration.
“Depuration” in layman’s terms is a purification process that’s used commercially and involves placing shellfish in tanks of clean re-circulating seawater, treating them with ultraviolet (UV) irradiation, and allowing them to purge their contaminants over several days.
The FSA said that although norovirus contamination can be an issue for a range of foods, norovirus in oysters does present a particular risk to consumer safety as oysters are generally consumed as a raw product so the virus is not destroyed before consumption by heat processes such as cooking.
David Jarrad, director of the Shellfish Association of Great Britain (SAGB), is highly supportive of the FSA’s move but stresses that oysters receive unjust press.
It would be wrong to “bury our heads in the sand” and say there’s no issue with norovirus and shellfish, because when you’re eating raw products there’s the potential for viruses or bacteria within the water column to end up on the diners’ plate, he said.
“However, when you look at the statistics of norovirus illnesses, 97 percent of incidents in society are due to person-to-person contact, so only 3 percent is foodborne and of that 3 percent, the vast majority is infection passed by infected food handlers.”
The amount of illnesses that come from the actual raw products, with the raw products being the causative agent, is “infinitesimally small,” said Jarrad. The problem is that nobody wants to blame the people handling and preparing food and so the shellfish “invariably take the blame.”
The U.K. National Health Service (NHS) describes norovirus as a “mild” illness that usually lasts up to 48 hours. The trouble is that because it’s highly contagious, statistically one in six people in the United Kingdom are actively shedding norovirus.
Nevertheless, the SAGB would like to see substantial funding go toward much needed depuration research. UV depuration has been around since the 1970s and while the process is extremely effective at removing bacteria, science has moved on to the point that individual viruses can be successfully identified, said Jarrad.
He concedes that with just four associated outbreaks in two years, it would be difficult to prove that any new measure had benefited the cause, but should an FSA-backed study establish an affordable solution that removed the problem of viruses, the U.K. oyster industry would have found its holy grail.
“There are a few universities that are definitely going to be interested in the project and if they do manage to pull the rabbit out of the hat and change the way we depurate then we would be delighted. It would be a way of demonstrating that we are doing everything we can to mitigate the risks,” said Jarrad.
Despite the dreaded n-factor, the U.K. oyster industry is thriving with strong consumer demand. Prices are also good, partly as a result of France’s production problems caused by the widespread ostreid herpes virus-1 (OsHV-1). The sector is also buoyed by the fact there hasn’t been any further outbreaks of OsHV-1 in U.K. waters since the one discovered in Poole Harbour, on the south coast, in October last year. This outbreak was just the third reported in the United Kingdom in four years.
Farmers are having a slight problem obtaining sufficient seed, because of the demand for seed and half-grown oysters from France, but the feelings are pretty good within the cultivation industry, said Jarrad.
