The number of confirmed cases of norovirus in England and Wales is 83% higher than this time last year, according to the latest figures from the Health Protection Agency (HPA).
There have been 3,046 confirmed cases so far this season, compared with 1,669 last season. The norovirus season runs from around November to April.
It has been estimated that for every confirmed case there are around 288 unreported cases, since the vast majority of affected people do not access health care services.
By that reckoning, almost 880,000 people could have been affected.