Norovirus could have hit 880,000 people Electron micrograph norovirus particles. Photograph: CDC/Phanie / Rex Features Almost 880,000 people could have been affected by an outbreak of the winter vomiting bug, health officials said. The number of laboratory-confirmed cases of norovirus is 83% higher than the same time last year, the Health Protection Agency (HPA) said. So far this season there have been 3,046 confirmed cases of norovirus in England and Wales, but for every reported case there are likely to be a further 288 unreported sufferers, the HPA added. Last season there were 1,669 cases. During the fortnight to 16 December there were 61 outbreaks in hospitals in England. The bug has swept the country and has led to the closure of dozens of hospital wards. It has also affected holidaymakers on two cruise ships. Norovirus is highly contagious and can be transmitted through contact with an infected person or contaminated surfaces and objects. It is known to spread rapidly in closed environments such as hospitals, schools and nursing homes. Symptoms include sudden vomiting, diarrhoea or both, a temperature, headache and stomach cramps. The bug usually goes away within a few days. Although people can suffer from norovirus at any time of the year, activity increases in the winter months, with most cases seen between January and March. The HPA said no two years of norovirus activity were alike. John Harris, an expert in norovirus at the HPA, said: "The number of laboratory-confirmed cases has risen again, following the drop in the number we reported last week. This is typical of the norovirus season where the number of laboratory reports fluctuates between October and April with the bulk of cases usually occurring between January and March. Norovirus is very contagious so we would urge anyone who thinks they may be unwell with norovirus to stay at home and stay away from hospitals and care homes. The infection is short-lived although it is very unpleasant while you are unwell. Most people will not need to go to see their doctor and will recover in a couple of days. It is important to take plenty of fluids to avoid dehydration.