Picture it: the Canadian National Expo. Nearly three weeks of carnival rides, horse shows, trapeze performances, and other flavors of Canadian frivolity. Where there’s a carnival, there must be carnival food, the more fried and ridiculous the better. (Disclaimer: I’ve never been to “The Ex,” but I’m extrapolating from my state and county fair experiences. The fried-food purveyors are always trying to outdo each other: fried oreos! Fried candy bars!) The CNE boasts an impressive array of fair food, but when people started to get sick, suspicion narrowed on a particular headline-grabbing indulgence: the cronut burger.
In creating the cronut burger, Epic Burgers & Waffles was trading on a popular obsession with the pastry, invented and named earlier this year by a New York pastry chef who combined features of the croissant and the doughnut (hence the name), filled the layers with cream, and offered it first in rose vanilla and then other flavors. Purists say Epic’s cronut burger is a shameless knockoff, sullying the name of cronuts everywhere.
But did it make anyone sick? Fair-goers began reporting to the hospital with symptoms of food poisoning, and sometimes long lists of food they had sampled. CBS News shared some typical stories:
One said his wife became sick after eating the cronut burger, as well as seafood chowder fries, ice cream waffles and a smoothie. He, however, did not get ill after eating a cronut burger.
Another man told CBC he felt ill after eating a cronut burger and a slate of other high-fat snacks that included a Canuck burger, sweet potato fries, poutine and a Philly cheesesteak.
Later Wednesday, CBC News spoke to a man who went to the CNE with a group of co-workers on Tuesday night. They all had fast food, but Kyle Burton said he was the only person to try the cronut burger.
But wait! Not everybody who ate the cronut burger got sick, and the people who did get sick had eaten more than just cronut burgers. At first I wondered if the cronut burger was framed. It was being accused before all the evidence was in: news reports fingered the burger on Wednesday but test results weren’t available until Friday. Meanwhile, Toronto Public Health announced they had “concentrated [our] investigation around one food premise located at the CNE,” namely Epic Burger and Waffles. How did they know?
The classic tool for this, in epidemiology, is the 2×2 table. You compare how many cronut-burger-eaters got sick compared to non-cronut-burger eaters, and see if cronut-burger-eating seems to increase your risk of illness. You can do the same for, say, seafood chowder fries or Philly cheesesteaks. It’s possible to eat a contaminated food and not get sick; some people’s immune systems may fight off the bug better than others. But if people are getting sick without eating the suspected food, it can’t be the culprit.
By Friday, Toronto Public Health was sure enough to make a statement: “The only common food consumed by those who were ill is the ‘cronut burger’ sold by EPIC Burgers,” they wrote. Furthermore, lab tests had confirmed that the burger contained a toxin produced by Staphylococcus aureus bacteria.
Staph aureus is a common resident on human skin, so a few cells in your burger shouldn’t be a big deal. But if contaminated food is kept at unsafe temperatures too long (in the “danger zone” that covers everything warmer than a fridge but cooler than a stove), the bacteria can multiply and begin producing a toxin. What’s more, that toxin is heat-resistant, so cooking the food can’t make it safe again.
The sick people’s symptoms fit with what we know of this toxin’s effects and timing. (It’s quick-acting, causing illness within hours; other high-profile foodborne illnesses like Salmonella take a few days to incubate.) Further testing will show whether a particular component of the cronut burger is to blame. Cream-filled pastries are a common source of Staph aureus poisoning, so that would be my bet.