Four wards at the Royal Bournemouth Hospital have been affected
Five wards have been closed to new admissions at two Dorset hospitals after an outbreak of the vomiting and diarrhoea bug Norovirus.
Four wards at the Royal Bournemouth Hospital and one at Christchurch Hospital have been affected.
Health chiefs recommended people should not visit patients in these wards, while visiting is restricted to next of kin only in all other areas.
Sixteen procedures have been re-arranged due to the outbreak.
Belinda Atkinson, director of nursing for the Foundation Trust, said: "While we regret the inconvenience and upset that restrictions on visiting can cause friends and relatives, this is absolutely essential to ensure the virus does not spread to other parts of our hospitals.
"The safety of our patients is paramount and the cooperation of members of the public in helping this is appreciated."
The hospital said the situation was being reviewed twice daily.