A new method unmasks noroviruses on food
Nausea, vomiting, diarrhoea, fever: a lot of people will be familiar with the evil effects of a delicious dinner party the night before. Noroviruses might be the causative agents of this suffering. In many cases, it is difficult to determine where the viruses come from. The Chemical and Veterinary Investigation Office (CVUA) in Stuttgart has now developed a method that enables the detection of these malicious viruses on food.
A typical case study for Matthias Contzen and his team from the CVUA (Chemisches und Veterinäruntersuchungsamt) Stuttgart involves the testing of between 50 and 200 samples of food from a single dinner party. The institute’s biologists and veterinarians at the Fellbach laboratory have, with such studies, succeeded in developing a method that enables the detection of noroviruses on food.
The preliminary report by food inspectors gives the researchers an initial idea of what they have to look for. “This gives us an idea of which viruses might have contaminated the food,” said Contzen. The food is packaged and registered and then examined for the presence of viruses, which is a very awkward and time-consuming process. As little as 25 grammes of a dish is sufficient to extract a concentrated virus solution, which is, however, very unstable. “We have to be very careful, otherwise the sample will rapidly become unsuitable for the detection of viruses,” said Contzen.
Looking for noroviruses
The researchers are looking for typical norovirus characteristics. Specific signals will substantiate the initial suspicion. Another method will subsequently be used to determine the actual norovirus species that might have spoiled the food. The “winter vomiting disease” is spreading extremely rapidly, but is also prone to very rapid changes. That is why any vaccination against this virus proves ineffective. As soon as the results of the food analyses are available, they will be compared with the stool samples of those suffering from the illness. “If the viruses in the food and stool samples are identical, then it is clear what has caused the sickness and our job is finished.”
A huge demand
Funded by a grant from the Landesstiftung Baden-Württemberg foundation, Contzen and his colleagues have spent four years developing this method. Experts estimate that up to 40 per cent of norovirus infections are transmitted by food. Previously, there was no method available for reliably detecting these viruses on food. The Fellbach researchers’ method therefore serves as a model. However, a rapid test that could be used by food inspectors to carry out on-the-spot tests in restaurants or supermarkets, is still far in the future. “Our model kit does however provide us with excellent results and enables us to develop a national standard for the detection of noroviruses in food,” said project leader Contzen with a certain amount of pride.
There is a huge demand for norovirus testing methods. About 10 years ago, noroviruses were only known to scientists. Since then, the virus, which is transmitted by person-to-person contacts, has been spreading rapidly. The Robert Koch Institute estimates that more than a million people will be infected with noroviruses this year alone. Although vomiting and diarrhoea only last for about two to three days, the huge loss of liquid could be dangerous for children and the elderly. Also, those who have been infected with the viruses will not become immune to the pathogen as a result.
Hygiene, i.e. hand washing is the only effective option to reduce the spread of norovirus pathogens. Cooks, waiters, party service staff and party hosts must always bear in mind that group situations where a lot of food is handled are perfect environments for noroviruses to proliferate and spread.
The analysis of the dinner party buffet eventually showed that the viruses did not come from the party service. The catering company had taken all the necessary hygiene precautions. On this occasion, the food inspectors were unable to say who had had their fingers in the pie.