Norovirus: 100,000 struck down over Christmas For every confirmed case, the HPA estimates another 288 go unreported, as most people do not bother to visit their doctor when they have the winter vomiting bug, which also causes diarrhoea. John Harris, a norovirus expert at the HPA, said: "As we have seen in previous years there has been a dip in the number of confirmed laboratory reports owing to the Christmas and New Year period. However, in line with other norovirus seasons we will expect to see an increase in the number of laboratory reports in the next few weeks. He continued: "Norovirus is very contagious, and anyone who has had it knows it is very unpleasant. If you think you may have the illness then it is important to maintain good hand hygiene to help prevent it spreading. We also advise that people stay away from hospitals, schools and care homes as these environments are particularly prone to outbreaks. The total number of norovirus outbreaks in hospitals this season has reached 590, of which 517 led to ward closures.