At a New Year’s Eve dinner organised by a local hotel for 270 people, 56 guests, hotel staff and residents fell sick from an outbreak of gastroenteritis that was caused by raw oysters that were contaminated by norovirus, Public Health Department manager John Attard Kingswell said yesterday.

Speaking at an information conference on norovirus – one of the main causes of gastroenteritis – Mr Attard Kingswell said that when the various food items on the menu were analysed, compared to the other food items, the oysters were at a very high risk.

The oyster samples sent to a laboratory in Rome, he said, had the same strain of norovirus that was found in the people who fell sick.

Recent scientific findings reveal that norovirus causes around 50 per cent of all gastroenteritis (stomach pain, diarrohea, and vomiting) around the world. The virus is named after the place where the outbreak occurred in Norwalk, Ohio, where in November 1968 an outbreak of acute gastroenteritis occurred among children at an elementary school.

Common names of the illness caused by noroviruses, previously called Norwalk-like viruses, are winter vomiting disease, viral gastroenteritis, and acute nonbacterial gastroenteritis. It is also incorrectly labelled as food poisoning, and in American slang it is stomach flu. The virus can cause symptoms such as stomach pain, diarrohea, and vomiting in humans, as well as general lethargy, weakness, and muscle aches.

Mr Attard Kingswell said the Public Health Department strongly recommended that all forms of seafood should not be eaten raw, but be cooked.

He pointed out that norovirus was usually found in seafood, water, ice cubes and prepared food.

Public Health medical official Anthony Gatt said that according to the European Centre for Disease Prevention and Control, the number of norovirus outbreaks in 2006 in hospitals and other public areas increased.

“The most common method of transmission is person-to-person,” he said.

Dr Gatt pointed out that Malta was not an exception to norovirus as in 2006 the Public Health Department was informed of outbreaks in the hotel industry, St Luke’s Hospital and several households.

According to a reply by Health Minister Louis Deguara to a question in parliament made by Labour MP Michael Farrugia in November, there were 47 cases of gastroenteritis in St Luke’s Hospital caused by norovirus, two of the cases were hospital staff.

During 2006, there were four reported outbreaks of norovirus in hotels – one of which was not confirmed, said Dr Gatt.

Furthermore, he added, there were two outbreaks in refugee centres and two outbreaks at old people’s homes. There was a particular hotel that had four outbreaks in one year – in March, April, June and October, said Dr Gatt.

Dr Gatt spoke about the importance of clean habits in hygiene.

One of these outbreaks was caused by a tourist who fell sick on the way to the hotel from the airport, he explained.

“He did not inform the hotel staff about his condition and let four days pass. Had the staff known, the tourist would have been confined to his room until the outbreak was over. It was only four days later, when he called a doctor, that the hotel knew that there was an outbreak of norovirus. However, the virus was spread to other people in the hotel,” said Dr Gatt.

Cruise ships still continue to be a carrier for this disease and provide a steady supply of new susceptible passengers on a regular basis, said Dr Gatt.

The most important way of limiting the norovirus outbreaks was prevention, as opposed to decontamination, he said.

The virus is commonly transmitted person-to-person, touching contaminated surfaces, ingesting contaminated food and water, and swimming in contaminated water, explained Dr Gatt.

It is a very resistive virus with an infective period of around two weeks. It is not killed by alcohol and the normal concentration of chlorine found in tap water, he added.

Furthermore, it is resistant to sub-zero temperatures and is only killed by temperatures higher than 60 degrees Celsuis.

The possibility of outbreaks are reduced 50 per cent through proper handwashing, he said.

Common areas needed to be cleaned thoroughly and people working in the hospitality industry needed to be sent home as soon as they showed the first symptoms of norovirus infection, said Dr Gatt.

“Do not hesitate to send your staff home immediately – after all it is for your own good,” he said. “They should come back to work only two days after the last symptom has manifested itself.”