The number of UK people hit by winter vomiting bug norovirus could now stand at more than a million, it is estimated.

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The number of laboratory-confirmed cases of the norovirus has reached 3,538 in England and Wales, up from 3,046 last week and an 83 per cent increase on the 1,934 cases at this time last year, the Health Protection Agency has confirmed.

But the HPA has said that for every reported case an estimated 288 go unreported, meaning there could be 1.01 million cases in total, up from just under 880,000 last week. The HPA said that in the two weeks to 23 December there were 70 reported hospital outbreaks of the virus, compared to 61 in the previous fortnight, bringing the total of outbreaks for the season to 538.

The number of cases has risen earlier than expected this year, following an as-yet unexplained trend seen across Europe and other parts of the world. John Harris, an HPA norovirus expert, said: "The number of laboratory confirmed cases has risen once again as it appears that we have seen the rise in cases that usually begins in January start a little earlier than we normally expect.

"Norovirus is very contagious, and very unpleasant.

"To help prevent spread of the disease, it's important that people who believe they are unwell with the virus maintain good hand hygiene and stay away from hospitals, schools and care homes, as these closed environments are particularly prone to outbreaks which can cause severe disruption."

Science Reporter Asha Tanna said: "The HPA also says 25 per cent of the population will suffer from some sort of gastro-intestinal each winter. This is the peak time for the norovirus."

Read more: Norovirus - the key questions

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.

Bug goes within a few days

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 Royal Lancaster Infirmary was one of the latest hospitals affected. It closed all its wards to visitors for two days on December 19 in a bid to stem a "significant outbreak" that saw 140 patients and 20 staff affected by symptoms of the bug.

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