People suffering from a winter vomiting bug should stay at home until they have recovered, health experts said today.

Cases of norovirus, which causes sickness and diarrhoea and is highly contagious, have closed some hospital wards across the country.

The number of reported cases of norovirus is lower than the same period last year, the Health Protection Agency (HPA) said as it sought to quell reports of a crisis.

It recommends anyone affected by the bug stays at home until the symptoms have passed.

The agency said it was seeing "fairly typical" levels of norovirus for this time of year, including some outbreaks in hospitals and schools.

"There is no reason at this stage to believe that there are more cases of norovirus than normal," it said.

Since July, there have been 1,575 confirmed norovirus cases, compared with 1,920 over the same period last year.

Norovirus is the most common cause of sickness and diarrhoea in England and Wales and the number of cases typically begins to rise in the winter months.

People usually recover within one or two days and many do not consult their doctor, meaning official figures only represent a fraction of the total number affected.

The disease has historically been known as the "winter vomiting disease".

The HPA recommends good hygiene to prevent people spreading the virus to others.

This includes thoroughly washing hands after going to the toilet and before and after preparing food.

Those stricken by the illness should avoid preparing food until 48 hours after their symptoms have disappeared, according to the HPA.

There is no specific treatment for norovirus but people are advised to stay at home and rest and drink plenty of fluids to prevent dehydration.

Professor Mike Catchpole, director of the HPA's centre for infections, said: "Norovirus is highly infectious and easily spread in settings where people are in close contact with one another so good hygiene, including frequent hand washing, is really important.

"Unfortunately there is no specific treatment for norovirus apart from letting the illness run its course.

"Thankfully most people will make a full recovery within 1 to 2 days but it is important to drink plenty of fluids during that time to prevent dehydration especially in the very young or elderly."

A spokeswoman for the Norfolk and Norwich University Hospital said visitors had been banned following an outbreak of norovirus.

Three wards are closed to new admissions and patients on another five wards are also affected by the bug.

Dr Judith Richards, consultant medical microbiologist at the hospital, said: "We are closing the hospital to all visitors in order to protect our patients from this bug which is circulating in the local community."