We will never know for certain what caused a large, multistate outbreak of E. coli O157:H7 infections linked to Wendy’s restaurants late last year, according to a new study led by investigators at the Centers for Disease Control and Prevention.
The study, highlighting weaknesses in our ability to respond to foodborne outbreaks, lands amid a separate report published by the CDC finding that, in general, we’re also failing to prevent outbreaks. In fact, cases from some common foodborne pathogens have increased relative to pre-pandemic levels.
In the outbreak last year, which spanned from July to August, at least 109 people in six states fell ill, with 52 needing to be hospitalized. Eating at Wendy’s was a clear link. But it wasn’t enough to crack the case.
The prime suspects were beef and leafy greens, common culprits in such an outbreak. Of the 68 people sickened in the outbreak who could give detailed reports of what they ate, 78 percent reported eating beef patties, and 68 percent reported having romaine lettuce on sandwiches. With that information, the US Department of Agriculture and the Food and Drug Administration tried to trace specific products back to their sources. Still, all traceback efforts failed to identify a single production lot that could explain the cases. And the restaurant cluster pattern made it impossible to triangulate a common food source.
Failures
In the postmortem on the outbreak investigation—published in the latest issue of the CDC’s Morbidity and Mortality Weekly Report—investigators noted several challenges that kept them from identifying the source. One was that some of the implicated Wendy’s restaurants had food handlers that became infected, creating the possibility that they themselves became a source of contamination, muddling the true source of the outbreak. There was also the fact that multiple menu items shared multiple ingredients.
Another problem was that the outbreak appeared limited to Wendy’s patrons. If there was an independent cluster of infections that genetically linked back to the E. coli O157:H7 seen in the outbreak, investigators would have had a better chance of triangulating the source. It’s possible there was such an independent cluster that went unreported. Many people recover from an E. coli infection without needing medical care and without reporting their case.
“The true number of sick people in this outbreak is likely much higher than the number reported, and the outbreak may not have been limited to the states with known illnesses,” the CDC said in its final outbreak update.
The bright spot of the response, the investigators reported, was that health officials responded promptly, leading Wendy’s to pull suspect lettuce from their restaurants. No other cases were reported after the lettuce was pulled, they noted.
The point is cold comfort in light of a separate report from the CDC showing that the US is failing to reduce foodborne infections across the board. Though cases of foodborne illnesses plummeted during the COVID-19 pandemic, illnesses from foodborne Campylobacter, Salmonella, Shigella, and Listeria rebounded in 2022, back to levels seen in between 2016 and 2018. Meanwhile, cases Shiga toxin-producing Escherichia coli (STEC)—which was behind the Wendy’s outbreak—increased relative to pre-pandemic years. Cases of Yersinia, Vibrio, and Cyclospora illnesses were also higher.
The report noted that reducing contamination of poultry and leafy greens would go a long way toward knocking back cases and outbreaks. But it would require “collaboration among food growers and processors, retail stores, restaurants, and regulators,” the report said.
