The Christmas party when seafood researchers gave themselves food poisoning

Friday, 13 December 2013: It’s morning, and Arne Duinker is busy preparing the food that he and his colleagues will enjoy at their annual Christmas party a few hours later. Duinker, whose day job is as a seafood researcher, is working with a few colleagues and some professional seafood chefs.

Little do they realise that it will all go horribly wrong.

“This was the first Christmas party where we decided to make seafood for everyone, and we wanted to do it ourselves”, explains Duinker.

In 2013 he was working at the National Institute of Nutrition and Seafood Research (NIFES), which has now been merged with the Institute of Marine Research (IMR).

Carpet shell soup

When the researchers and chefs are planning the menu, someone suggests using cockles in one of the dishes.

“I pointed out that you could only get imported cockles from Spain at that time. But what about using some local carpet shells from Øygarden instead? Everyone agreed that was a good idea”, says Duinker.

The researchers and chefs spend the whole day preparing the food together.

“We treated it as a cooking course, really”, says Duinker.

When they get to the carpet shells, he tells his fellow chefs that a few days earlier they tried steaming them, but that made them chewy and unappetising. As they are best served raw or slightly heated, they agree to use them in a shellfish soup where hot stock will be poured over the raw bivalves.

Good atmosphere and good food

Evening comes, and everyone has a great time at the Christmas party.

“The atmosphere was excellent and the food was delicious”, says Duinker.

Then, over the course of the weekend, things start going wrong.

Duinker spends Monday at home with a slightly bad back, but he sends some messages to his colleagues.

“That’s when I started to realise that it had all gone wrong”, he says.

A surprising number of people are off work that day, and Duinker and his colleagues soon identify a suspect.

“The symptoms indicated a classic case of gastroenteritis.”

When Duinker realises that in all likelihood many of his colleagues have got food poisoning from something they ate at the Christmas party, his scientific instincts kick in. Now they have to find out as much as possible.

Safely over the Atlantic

While the Christmas party is going on, Bjørn Tore Lunestad is sitting on a transatlantic flight. He is on his way home from a work trip to Cuba.

“When I came to work on Monday, there were quite a few conversations in the corridors. Lots of people weren’t feeling well”, he says.

Normally when there is an outbreak of this kind, people think that they are the only one to be suffering. So Lunestad notices a spot of relief when people find out that they aren’t the only ones to be suffering the classic signs of a stomach virus: vomiting, diarrhoea and a slight fever.

“I thought that it was all really interesting. And then we thought maybe we could link it to the Christmas party”, says Lunestad.

His specialist field is food microbiology, covering microorganisms such as viruses and bacteria in seafood. Lunestad realises that the incubation period, from the Christmas party until people have become ill, is a perfect match for norovirus.

“So then I thought that maybe we can learn something from this. At the very least we needed to investigate what the problem was”, he says.

The crucial carpet shell

His first task is to find out whether there really is a link between the outbreak of gastroenteritis and the Christmas party. He therefore performs a so-called “case control” study, where he interviews the people who have become sick and those who haven’t. Lunestad does this by sending a questionnaire to all of his colleagues at NIFES. He asks them whether they attended the Christmas party and whether they have become ill. Finally he asks them to select the items that they ate at the Christmas party.

When Lunestad analyses the responses, he finds the guilty party. For almost all the dishes, there is no link between who has eaten it and who has become ill. With one exception: the carpet shell soup.

“I told Arne Duinker about this. He said that he happened to have a single carpet shell left in the fridge”, says Lunestad.

The one remaining carpet shell is immediately sent for analysis to the Faculty of Veterinary Medicine at the Norwegian University of Life Sciences.

“They found quite high values of two different strains of norovirus”, says Lunestad.

Decided against stool samples

Now the researchers are almost certain who the guilty party is. The shellfish soup has been identified, and norovirus has been found in the one remaining carpet shell.

“The only thing really missing was to get stool samples from the people who had become ill. Either that or vomit specimens, as they both contain the virus. I did consider it, but then I decided that it wasn’t fair to subject everyone to that”, says Lunestad.

Of the eighty people who attended the Christmas party, forty suffered varying degrees of illness. A norovirus infection usually stays in your body for anything from one day to just under a week, but in many cases it feels like it stays with you longer than that. You only need a few virus particles to become ill, so norovirus is highly contagious.

“Some people became really ill, and also infected other family members in several rounds of transmission. So they still didn’t have much appetite during Christmas”, explains Duinker.

The cup absorbed the heat

But how could this happen? After all, boiling soup had been poured over the shellfish.

“When you put shellfish in a cup, and then pour boiling soup over it, clearly any bacteria and viruses will be put out of action. Or so we thought”, says Lunestad.

But is that true?

The next stage of the “investigation” of the Christmas party disaster is a reconstruction. Lunestad and Duinker find a cup similar to the one in which the soup was served, put some onion in it and add a piece of carpet shell with a thermometer probe in the middle of it. Then they pour the boiling soup in, and watch the temperature rise.

“It turned out that the cup weighed around 230 grams, while the soup and other ingredients were lighter. So the mass of the cup and the cold ingredients meant that the temperature actually didn’t get that high”, says Lunestad.

The core temperature of the carpet shell piece never exceeded 49 degrees, which is not enough to deactivate a virus.

“It seemed so improbable. When you pour boiling soup into something, you think that anything in there will die”, says Lunestad.

One important lesson was therefore that you must not underestimate the ability of porcelain, cups and other cooking equipment to absorb heat when making this kind of dish.

A difficult virus to research

The reconstructions also provided important information about norovirus. The reason it is so valuable is that scientists have been unable to cultivate this type of virus.

“This means that it hasn’t been straightforward to investigate the temperature at which the virus becomes harmless”, says Duinker.

As a result, there was not sufficient data on the temperature tolerance of norovirus.

“But now we could at least document that heating the virus to approximately 50 degrees is not enough to inactivate it”, says Duinker.

There is still a shortage of data on how high the temperature does need to be to make norovirus in shellfish harmless.

Harvested after heavy rain

The possibility of there being a virus in the shellfish they would be eating hadn’t even crossed Arne Duinker’s mind. This was because the shellfish came from an approved location in Øygarden, which had been investigated for intestinal bacteria.

“I contacted the supplier of the carpet shells, and it turned out that there had been heavy rainfall the week before the Christmas party, when they were harvesting our carpet shells”, says Duinker.
 
This had probably caused sewers in Øygarden to flood, and he believes that this may have resulted in unusually large amounts of sewage entering that part of the sea.

Novovirus and Pacific oysters

In parallel with the work of Lunestad and Duinker, the Norwegian bivalve industry has introduced new methods to combat norovirus.

“One of the methods used today is keeping the bivalves in virus-free water for three weeks”, says Duinker.

Nevertheless, norovirus in bivalves remains a problem, not least on account of the Pacific oyster. That’s why Mette Myrmel, a norovirus expert from the Norwegian University of Life Sciences, has been taken on in a part-time role at the IMR. In addition, a research scholar will be hired to study norovirus in shellfish.

“We are focusing on this area, greatly helped by our experience with the Christmas party. Now we aim to learn much more about the subject, so we can provide the right advice to people who collect Pacific oysters, for example”, says Duinker.

An article on the experience from the Christmas party outbreak and the subsequent findings were published in the scientific journal “Food and Environmental Virology” in December 2016.

Its publication was celebrated with carpet shells and champagne.