The Centre for Health Protection believes Norovirus is behind the recent food poisoning of 33 people who ate raw oysters. One of the victims has tested positive for the virus.

They all came down with abdominal pain, diarrhoea, vomiting and fever after eating oysters in four different outlets September 22 to October 5.

The oysters are believed to be from the same supplier. The Centre for Food Safety has taken 15 samples from the supplier for testing, and asked for its oyster distribution list and the product's source.

The virus usually exists in seafood, especially raw oysters. The seafood trade should be aware of the situation and stay vigilant. Retail outlets should:

* obtain oysters from credible sources;

* use separate equipment for the preparation of oysters; and,

* keep oysters separated from other food items at a temperature between zero and four degrees Celsius.

So far this year 75 suspected food poisoning cases affecting 303 people who ate raw or undercooked oysters have been reported. The figures for 2005 were 70 cases affecting 329 people.