Health officials are investigating the cause of an "unusual" salmonella outbreak which has struck down more than 20 people.
Birmingham's Heartlands Hospital said its wards were treating eight patients, who are all in a stable condition, for the effects of the bacteria.
Four staff members at the hospital and 19 patients have so far tested positive for a common strain of salmonella, prompting fears of a more widespread community-based outbreak.
Restrictions have been put in place on visitors to eight wards at the hospital, and deep-cleaning processes have been put in place.
A hospital spokesman said stringent testing had not highlighted any signs of the salmonella bacteria in hospital food or water.
Dr Andrew Catto, the hospital's medical director, said: "Any infection in someone who is already ill can be very serious and we are taking every precaution possible to protect our patients and staff.
"We are concerned by the spread and number of patients who have tested positive, as this is unusual.
"Not all community salmonella cases get reported, as many people recover quickly and do not feel the need to go to see their GP.
"Usually, we see between two and four cases across the West Midlands reported monthly and for a hospital to see this number in such a short space of time requires expert investigation."
All visitors to the hospital are being asked wash their hands on entry and exit from any ward area, and advised not to visit the site if they have had diarrhoea or vomiting within the previous 48 hours.