A restriction on visitors has been put in place at the Royal Berkshire Hospital after an outbreak of the winter vomiting bug norovirus.
Some planned surgery has also been delayed, but outpatient appointments and day surgery remain unaffected.
The health trust said visiting times to wards were "significantly limited".
The trust said it anticipated the situation would improve over the next few day but the virus could affect the community for weeks.
Dr Jonathan Fielden, medical director, said: "Every year we must manage a period of time when norovirus hits our community.
"We know that many schools, nursing homes and other workplaces are already affected and inevitably we are now experiencing issues within our trust."
The trust said it was allowing essential visits only, for example parents of children on paediatric wards or close relatives of seriously ill patients.