Three wards have been closed at the Princess Royal Hospital following an outbreak of sickness and diarrhoea.
The norovirus bug has affected 17 members of staff and 35 patients at the Haywards Heath hospital.
Visitors are being asked to observe ‘good’ hygiene and hand washing.
Balcombe, Ardingly and Pyecombe wards are not taking in any patients and isolated cases of the bug have been noted on Ansty, Newtimber and Horsted Keynes wards.
A spokeswoman for Brighton and Sussex University Hospitals NHS Trust, said: “Strict infection control measures are in place at Princess Royal Hospital to prevent the spread of symptoms and the general public are asked for their support in helping us maintain these.
“Anyone with symptoms of diarrhoea or vomiting should not come to hospital but should contact their GP surgery, the out of hours GP service or the 111 service for advice.”
Staff at the Princess Royal are urging people who might have norovirus to stay at home to protect ‘vulnerable’ patients at the hospital.