08/22/2013 08:44 EDT | Updated 10/22/2013 05:12 EDT

CNE cronut burger stand stays closed amid public health probe

Toronto Public Health officials are in their second day of investigating a health scare that has forced the precautionary closure of a vendor who had been selling cronut burgers at the Canadian National Exhibition.

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Thirty-four people have reported symptoms of food-borne illness after eating at the fair on Tuesday. Paramedics treated 12 people and recommended that five be taken to hospital.

A common source of the illness has not been confirmed, but some of those who became sick told officials they had eaten at Epic Burgers and Waffles, the vendor that makes the trendy cronut hamburger, which features a croissant-doughnut mix for a bun.

The food outlet has been closed as a precaution. The move follows an order by the CNE, not Toronto Public Health.

Epic Burger was subject to a three-hour inspection on Wednesday morning, though health officials said it has still not been determined what vendor or food may have made people sick.

Health expert suspects toxin in food

Based on news reports of patients' symptoms, Tim Sly, a professor at Ryerson University’s school of occupational and public health, said he suspects the illnesses were caused by a toxin in the food due to the short time between when it was eaten and when patients reported feeling sick.

“With short onset times, you're looking at something that may have grown in the food and survived the cooking,” he said in an interview Thursday on CBC Radio’s Metro Morning.

"I'd put my money on a poison or toxin that has grown in the food, and then it doesn't matter if the food is cooked. It's still going to be there."

While Sly said most of these types of food contamination are not fatal, they cause discomfort for patients.

“You're not sure which end to put over the toilet,” he said.

Toronto Public Health will test food samples from the Epic Burger vendor, but the results won’t be available until Friday at the earliest.

In the meantime, the Epic Burger stand at the CNE will remain closed.

The Ex opened last Friday and runs through Sept. 2. It typically draws more than a million visitors each year.

In recent years, the Ex has offered a number of unusual food items, including deep-fried butter and bacon milkshakes.