About 45 employees at the hospital came down with gastrointestinal symptoms, including diarrhea, cramps and fever, after eating food that may have originated in an in-house catering service that is only used by staff.
The service is run by the hospital's Atrium Café, a franchise operated by a volunteer auxiliary, which also serves hundreds of staff and visitors to the hospital each day.
The coffee shop is independent of the hospital's main cafeteria.
"We closed the coffee shop immediately on Thursday afternoon," said hospital spokesman Glenn Nashen. "Tests were done all day Friday, and although nothing has been conclusive at this point, the suspicion is that [the virus] may have come from this catering service."
Nashen said as far as the hospital knows, only staff at the hospital caught the virus.
So many staff members in the neurology department fell ill that the neurology clinic had to be closed for half a day on Thursday and all of Friday.
The neurology clinic is expected to be open again on Monday.
Until the infection prevention and control team determines the specific cause of the outbreak, the coffee shop will remain closed, Nashen said.