People are being urged to stay away from local hospitals if they are suffering from diarrhoea and/or vomiting.
Three wards continue to be affected after outbreaks at Scunthorpe and Grimsby hospitals.
At Scunthorpe hospital wards 22 and 16 are closed to new admissions but ward 24 has now reopened after a deep clean.
Meanwhile at Grimsby hospital ward C1 Holles remains closed. All tests so far have confirmed that the virus is Norovirus.
Staff and visitors who have been suffering from diarrhoea or vomiting are urged not to come to hospital until they have been symptom-free for 48 hours, as they will be infectious to others during this period.
There's no specific cure for the illness, which is usually mild and shouldn't last more than a couple of days.
If you have symptoms of diarrohea and/or vomiting you should follow this advice:
· Drink plenty of water to avoid dehydration
· Take paracetamol for any fever or aches and pains
· If you feel like eating, eat foods that are easy to digest
· Stay at home – don't go to see your GP because diarrhoea and vomiting is contagious and there's nothing your GP can do while you have it
· Contact your GP to seek advice if your symptoms last longer than a few days or if you already have a serious illness.