The extent of the C. difficile outbreak in Ontario hospitals will be revealed on Friday but Premier Dalton McGuinty faced harsh criticism today for doing too little, too late.

More than 500 people have died in several hospitals across the province after they became infected with the bacteria. However, opposition parties say they suspect thousands of people have actually died because of the outbreak.

At Queen's Park on Wednesday, opposition parties asked McGuinty why he didn't take action against the bacterial outbreak years ago. They demanded a formal investigation into the case.

"(Prime Minister) Stephen Harper is going to call the inquiry into listeriosis, you demanded the inquiry into SARS and it was provided," said Elizabeth Witmer, the Conservative health critic in legislature on Wednesday. "We have over 500 deaths in just a fraction of our hospitals and you refuse to take action."

However, McGuinty says he's hired 137 new infection-control staffers and has ordered all hospitals to take extra precautions in keeping their facilities sanitized to prevent C. difficile infections.

"We think that when you go to a hospital or you (put someone in a hospital), you don't want them to get sick as a result of that experience," he said. "We understand that and we're going to do everything we can, working with experts and following their very best advice, to limit the influence of C. difficile."

A study on the C. difficile reporting, by the Ministry of Health and Long-Term Care, comes out on Sept 26. The findings were expected to be released on Sept. 30 but the ministry announced the earlier release date on August 21.