Norovirus is highly contagious
The winter vomiting bug could spread rapidly across England unless people are sensible and stay at home when they have the virus, a leading GP warns.
Many hospitals have already been forced to close wards to try to control outbreaks of norovirus.
Experts say norovirus is on the up but this is not unusual for the season, despite media reports of a crisis.
People should stay off work for 48 hours after the symptoms go, says The Royal College of GPs' chairman.
They should also stay away from doctors' surgeries and hospitals to avoid spreading it to others, advises Professor Steve Field.
Scotland, Wales and Northern Ireland have not seen any increase in cases of norovirus.
Last year more than 3m people had the bug, which also causes diarrhoea and is spread through contaminated surfaces.
Although unpleasant, the illness is not usually dangerous and people usually recover fully within two to three days.
The very young and very old are most at risk of complications from dehydration.
The bug thrives in confined environments such as hospitals, nursing homes, schools and cruise ships, but can be beaten by good hygiene.
It can be spread by contact with an infected person, through contaminated food or water or by contact with contaminated surfaces or objects, such as door handles.
Professor Field said: "If people heed the advice then we can minimise the number of people who will get it.
"If people are going down with diarrhoea and vomiting they should stay at home and drink plenty of fluids. It will not last long - for the majority of people it lasts a day or so.
Areas with hospitals that have closed wards or restricted admissions to contain norovirus over the last couple of weeks
Norfolk and Norwich
Wigton and Alston
"Obviously we worry about very young babies, the very old and people who are immunocompromised, but generally you do not need to go and see your doctor."
He said anyone who got sick should make sure they wash their hands thoroughly to prevent spreading the bug to others.
"If someone went to the toilet and did not wash their hands properly before touching a door handle and then you touched it, you could catch norovirus. The droplets stay on door handles and other objects for many hours.
"But norovirus is killed by disinfectant."
Professor Field said GPs and NHS Direct had also been seeing more people with flu symptoms, and said there could be a flu outbreak around Christmas - something far more worrying than norovirus.
The Health Protection Agency has seen an increase in reports of norovirus, but says this is typical for the season.
A spokeswoman said: "There is no evidence to suggest that activity this year will be any greater than last year."
Since July there have been a total of 1,575 confirmed norovirus cases, in comparison with 1,920 over the same period last year and 1,075 over the average of that period since 2005-2007.
But the HPA says this reflects only a proportion of the actual number of cases which will be seen in the population as the illness only tends to be of a short duration and confirmation requires a stool sample to be sent via their GP.
Katherine Wilson of the National Patient Safety Agency said: "We would like to remind all healthcare staff who have direct contact with patients to be extra vigilant during this current norovirus outbreak and ensure that they are following our recommended guidelines for hand hygiene."