The first signs of Christmas, the biting chill in the air - these are all signs that winter has arrived. Unfortunately alongside festive cheer, it also sees the start of the winter vomiting season aka the norovirus.
Experts are issuing warnings after a spate of health outbreaks.
There were 18 outbreaks of norovirus in English hospitals last month, all but one of which caused ward closures, Public Health England (PHE) said.
Closures can be very disruptive but are necessary to stop the spread of the highly contagious virus.
Typical symptoms of the vomiting bug include the sudden onset of projectile vomiting and watery diarrhoea. Some people might also experience headaches, a mild temperature and stomach cramps.
There is no treatment for the virus, but it is important to stay hydrated. Most people will recover within a few days.
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PHE said it was vital that people who suspect they have norovirus do not visit hospital or their GP.
John Harris, a norovirus expert for PHE, said: "For patients already ill in hospital, this virus could cause further health complications, making it vital to prevent introducing the virus into the hospital environment."
The virus is spread through contact with an infected person or with contaminated surfaces or objects, or by consuming contaminated food or water.
It spreads particularly quickly in closed environments such as hospitals, schools and care homes.
Between July 2013 and July this year, there were a total of 610 outbreaks in hospitals, 94% of which led to ward closures.
Mr Harris said: "October usually marks the start of the norovirus season and the bulk of cases will occur between now and April next year.
"No two norovirus seasons are the same and there is no way of predicting how busy a season will be.
"What we do know is that many people will be affected across the country and they will probably feel very unwell for a couple of days but will get better."