Schools across Burnley and Padiham are bracing themselves for the onslaught of norovirus, known as the 'winter vomiting bug' as cases are at a higher levels than expected.
A couple of primary schools have already been hit by the virus in Burnley with dozens of pupils absent.
And Burnley's largest school, Blessed Trinity RC College, has issued guideline letters to parents about what to do if their child falls ill.
In a letter sent out today parents are being advised to keep their children off school for at least 48 hours if they have been sick. This is to prevent the bug from spreading to other students and staff.
Acting on advice from the local authority the letter from the school, which has 1,250 students, also advises parents not to allow their children to return to their classrooms until they are fully recovered.
A spokesman for Blessed Trinity said: "We have no real concerns and the school will remain open as normal."
Cases of norovirus are at higher levels than expected at this time of year across Burnley and the North West, according to Dr John Astbury who is Head of Health Protection Cumbria and Lancashire, Public Health England for the North West.
And the advice to anyone suffering from the symptoms is not to visit their GP or hospital as they will usually make a full recovery within one or two days.
Dr Astbury said: " These higher levels are not unprecedented as norovirus activity varies from year to year and we continue to actively monitor the situation.
"One of the best ways to protect against norovirus is by practising good hygiene. This includes thorough hand washing with soap and warm water after using the toilet and before eating or preparing foods.
"Most people will make a full recovery within one to two days but it is important to drink plenty of fluids during that time to prevent dehydration especially in the very young, elderly or those with weakened immunity.”
Dr Astbury added that if anyone was concerned about their symptoms to contact NHS 111 or talk to their GP by phone.
The main symptoms of norovirus to look out for are:
* feeling sick (nausea)
* being sick (vomiting)
You may also have a high temperature of 38C or above along with a headache and aching arms and legs. Symptoms can start suddenly within a couple of days of being infected and it can be treated at home.
The advice is also to stay off school or work until the symptoms have stopped, for at least two days and also avoid visiting anyone in hospital during that time in case you pass the bug on to them.