A warning from Toronto Public Health officiails to those who may have eaten a sandwich from the Druxy's restaurant inside the Princess Margaret Cancer Centre.
Three cases are being investigated, where people may have contracted Listeria infections after eating at the restauant.
They say anyone who may have eaten there between January 1st and March 12th of this year, should keep an eye out for symptoms like fever, diarrhea, vomiting, nausea and cramps.
In those with weakened immune systems, like those who may have been at the hospital, are most at risk of developing a serious illness from a Listeria infection.
Officials say the restaurant is currently closed and being cleaned, with the owners co-operating with investigators.
On average, Toronto sees 17 cases of Listeria infection each year.