Bacteria in the cronut burgers sold by a Canadian National Exhibition food vendor caused roughly 150 people to become ill with food poisoning, according to Toronto Public Health.

The cronut burger, a beef patty between two doughnut-croissant pastries and topped with maple-bacon jam, had been the suspected source, but it was confirmed Friday afternoon.

"We do know from the vast majority of interviews we’ve done that people became ill directly after eating the cronut burger," said Dr. Dave McKeown, who is with Toronto Public Health.

McKeown said 150 people have now reported getting ill, some within a few hours, after eating at the CNE, up from 100.

Epic Burgers and Waffles, the creator of the cronut burger, voluntarily closed after the initial outbreak of illnesses early this week.

McKeown said staphylococcus aureus was present in lab tests performed on the burger, but officials were still trying to determine what specific ingredient was contaminated.

"Typically the bacteria multiplies in food in the presence of inadequate temperature control or inadequate food hygiene and food handling," McKeown said. "When the bacteria multiplies, it produces the toxin and it’s the toxin that causes the illness when ingested.

"The vast majority of people who ingest this toxin can recover quickly," he said, citing concerns for seniors and children.

The bacteria also doesn't have a particular smell or taste so CNE visitors who ate a contaminated burger wouldn't have known until the side-effects, which include nausea, diarrhea, and vomiting, were present.

CNE general manager David Bednar confirmed Epic Burgers would remain closed as the investigation continues.

"We have to let this investigation go full cycle," he said. "We've stopped this now. We're confident that it's over, however, going on into the future, whatever additional or different precautions may be necessary we're going to take them."

Three-hour inspection

On Tuesday, 12 people reported feeling ill after eating at the Food Building at the CNE, with five being treated in hospital. The number of those becoming ill after eating at the annual fair spiked as the week went on.

On Wednesday, Epic Burgers was subject to a three-hour inspection; the results of those tests were announced today.

"We have no evidence that any other product at the CNE is contaminated," McKeown said.

Toronto Public Health is now set to interview the remaining people who reported becoming ill and determine when the majority of the illnesses occurred.

McKeown also said it was "too early" in the investigation to determine whether any charges would be laid.

Epic Burgers posted a message on its Facebook page on Thursday saying it would co-operate fully with the investigation and the company stood by its staff and products.

"In the time that we've been operating at the CNE, we have had a clean bill of health and all our staff have been fully trained in food safety," the statement said.

According to Toronto Public Health, prior to the CNE opening food-handler training was provided to more than 1,600 workers, including those employed at Epic Burgers.

A spokesperson confirmed to CBC News that the food vendor was also inspected on the opening weekend Aug. 16 and received a pass mark.

Public health has inspected more than 300 food purveyors at the fair since then.