Visitors, staff and patients at Harrogate District Hospital are being urged to stay away if they feel ill, after an outbreak of norovirus has affected three wards.
Byland ward has been closed completely following an outbreak of the sickness bug, while the Acute Medical Unit and Jervaulx ward have also been affected.
Norovirus is so contagious that uninfected patients cannot be put in the same bay of beds as a patient with the sickness bug.
In a bid to control the outbreak, anyone with symptoms of the illness is being urged not to visit the hospital until they have been symptom-free for at least two days.
Director of Infection Prevention and Control Dr Jenny Child said: "It's extremely contagious, in a confined area like a hospital it can spread like wildfire.
"Young fit healthy adults can be knocked sideways an illness like this so you can imagine if you're frail elderly and feeling weak that can be really very difficult to cope with as well.
Although norovirus has rarely hit Harrogate District Hospital, Dr Child said that over the years many outbreaks at other hospitals have started by friends and relatives visiting patients.
Dr Child said that the most predominant symptom of norovirus is vommitting and/or diarrhoea.
Anyone who experiences these symptoms should wait until they have been sickness-free for at least two days before visiting the hospital.
Dr Child added: "Handwashing is one of the most important things we can do to help prevent the spread of norovirus.
"You should wash your hands before and after you go to the toilet, before you eat and especially after you clean up vomit or diarrhoea.
"Anyone who does become ill should keep drinking water and keep themselves well hydrated."