McGuinty's refusal came as officials declared the water system at the Seven Oaks Home for the Aged had been flushed and was again safe to use. The home's air exhaust system was also returned to service.
The air intake system is still being examined and remains shut down, Toronto's medical officer of health Dr. David McKeown said in a statement.
Conservative Leader John Tory has called for a formal inquiry to find what he calls "the full story" behind the outbreak at the provincial nursing home.
McGuinty dismissed the idea, but said he, too, wants to know exactly what happened.
Ontario Health Minister George Smitherman said last week that a review of the tragedy would be conducted by an independent third party.
The outbreak at Seven Oaks began on Sept. 25 and sickened 71 residents, 23 employees and 14 visitors to the nursing home. There have been no new deaths since Friday, and most of those affected continue to improve, McKeown said.
The home remains closed to new admissions and most visitors.