Oysters: are they safe to have on our menus?

Now the months have ‘R’s in them again we’re all free to enjoy oysters once more. After all nothing says luxury and opulence better than a flute of champagne and a plate of oysters freshly shucked and smelling of the sea.That is unless you spend the next two days camped in the toilet with severe vomiting and diarrhoea. The sad fact is that most UK oysters carry the risk of norovirus, a type of highly infectious virus that is the most common cause of food poisoning in the UK. The risk is great enough that many restaurants won’t put oysters on their menus. So what's being done about it? The Staff Canteen decided to find out.

Heston Blumenthal’s restaurant, The Fat Duck discovered just how disastrous they can be in 2009 when a norovirus outbreak from oysters, caused 529  people to report being ill. It was the biggest norovirus outbreak linked to a restaurant ever recorded and forced the temporary closure of the three-Michelin-star restaurant.

You would be forgiven for thinking that such a high profile incident would lead to something being done to eradicate the problem of norovirus in oysters but you would be wrong. Statistics from Public Health England show that from 2010 to 2012 there were 19 reported outbreaks of norovirus due to oysters. As most cases go unreported, the actual number is likely to have been much higher. Furthermore, according to studies by the Food Standards Agency (FSA) in 2011 76% of a sample of oysters taken straight from growing beds in UK waters had traces of norovirus present. This compares with 31% in Ireland(2009), 20% in USA (2006) and 5% in Holland (2007).

Why then is norovirus in oysters still such a large problem and why in the UK in particular?

“UK waters are badly polluted, amongst the worst in Europe,” says Dr Steve Kestin, managing director of oyster suppliers, The Cornish Shellfish Company. “The main reason is that we’ve got an inadequate waste water treatment process.”

Norovirus, according to Dr Kestin, is a human pathogen not naturally found in oysters or shellfish. The virus is found in human faecal matter which finds its way into waters where shellfish live and contaminates oysters as they feed and respire. The untreated human waste comes from combined sewer overflows (CSOs) which discharge raw sewage into UK rivers and coastal waters during heavy rainfall events to prevent the excess water in the sewage system backing up into people’s houses.

All commercial UK oysters must come from beds that pass standards set by the EU. Once caught they are also put through a purifying or ‘depuration’ process whereby they are kept in clean water for a period of time to remove any traces of pollutants. The problem, According to Dr Kestin, is that the EU standards for shellfish waters don’t include norovirus. Also nobody knows what a safe level of norovirus in oysters is. This means that depuration is an inexact science and the minimum period of depuration, as set by the Food Standards Agency (FSA), might not always eradicate enough of the norovirus to prevent oysters being infectious.

After The Fat Duck outbreak in 2009 Dr Kestin was approached by Gary Jones, executive chef of Raymond Blanc’s Le Manoir aux Quat’ Saisons, who asked him if he could find a depuration process that would prove 100% effective in removing norovirus from oysters.

Dr Kestin, who used to research food production at Bristol University, went away and came back with an enhanced purification process and norovirus testing to ensure the process had worked. Within six months Le Manoir had oysters back on the menu again.

So, problem solved? Not really according to Dr Kestin. The enhanced purification process costs more money and the norovirus tests cost over £100 each time, escalating his costs and more than doubling the price of his oysters. This means, as Dr Kestin said: “Very few outlets are prepared to pay the extra. We are considering discontinuing the brand as it’s not cost effective.”

So what does need to be done? According to Dr Kestin we need to limit how much raw sewage water companies can dump into our waters from CSOs as well as new EU legislation setting standards for norovirus in shellfish waters.

The problem comes from the Victorians according to Andrzej Nowosielski, a senior advisor at the Environment Agency. “The Victorians built our sewer systems,” he said, “so sewage and rain water go into the same pipes. During heavy rainfall this means the flow can be multiplied by 10, 20, 100, 1,000 times. The CSOs are a safety valve to prevent this backing up into people’s homes.”

There are about 15,000 CSOs in England and Wales, most of which discharge into rivers. Our sewage system contains some 589,000 kms of sewerage pipes. Since the 1960s most new homes have been fitted with new dual rain water and sewage systems but the vast majority – around 70% - of the UK’s sewage system is still the antiquated version bequeathed to us by the Victorians. Estimates about how much it would cost to fit new dual sewer systems across the country are often wild guesses, according to Andrzej but they usually involve figures around the £30 billion mark. There would also be the massive upheaval and cost to the environment of digging up the thousands of miles of pipes that criss-cross the country.

Water companies claim there is no hard evidence that norovirus outbreaks from oysters are due to sewage spills from their CSOs. However, according to a spokesperson from Water UK, which represents water companies, these companies recognise that limiting sewage spills from CSOs is generally a good thing to do. The water companies are currently putting together their plans for 2015-2020 which should, according to the spokesperson, include efforts to better manage CSOs.

Meanwhile everyone is waiting on changes to the EU Shellfish Waters Directive which should come into effect at the end of this year. However this won’t, according to Andrzej Nowosielski, include standards on norovirus in shellfish waters, due to difficulties in detecting what levels of norovirus are infectious.

At the moment then it seems to be a waiting game with – perhaps predictably – opposing camps expecting the other side to make the first move.

Speaking for shellfish suppliers, Dr Kestin said: “The water companies and Environment Agency aren’t doing nearly enough to control CSOs. If this was a chimney pumping pathogens into the environment and people were falling sick something would be done about it, but because it’s in the sea, nothing is done. In any other situation like this the polluter pays; why not in this case?”

Andrzej Nowosielski of the Environment Agency believes that the onus has to be at the other end of the chain, on better depuration processes. He said: “The only way I’m going to start eating raw oysters again is if there’s an effective depuration process. You could get a septic tank overflowing and it doesn’t matter how well the big sewage treatment works are going; you’ll still get norovirus in the water.”

Perhaps the last word should go to the restaurant that first asked for a foolproof depuration process because it wanted to continue selling safe, healthy and delicious oysters to its customers. “This is not a blame thing,” said Gary Jones of Le Manoir. “It will take everyone working together: the water companies, Environment Agency, government, shellfish companies, suppliers and chefs. Let’s have a debate with all parties involved… We are all in this together.”

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