Health experts are advising people suffering from the norovirus winter vomiting bug to stay at home until they have recovered.
Some hospital wards have had to be closed after the spread of the bug, which causes sickness and diarrhoea and is highly contagious.
The Health Protection Agency (HPA) has sought to quell reports of a crisis, saying that the number of reported cases of norovirus is lower than the same period last year.
The agency said it was seeing "fairly typical" levels for this time of year, including some outbreaks in hospitals and schools.
It added: "There is no reason at this stage to believe that there are more cases of norovirus than normal."
The number of cases of norovirus, which is the most common cause of sickness and diarrhoea in England and Wales, typically begins to rise in the winter months.
Official figures only represent a fraction of the total number affected, as people usually recover within one or two days and many do not consult their doctor.
The HPA recommends that anyone affected by the bug should stay at home until the symptoms have passed. They should also practise good hygiene, including thoroughly washing hands after going to the toilet, and before and after preparing food.
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