Outbreaks of Escherichia coli in several states have been linked to onions on McDonald’s Quarter Pounder hamburgers, following on the heels of a recall of Boar’s Head deli meat products linked to Listeria monocytogenes earlier this year. Such outbreaks expose vulnerabilities in the food supply chain and present opportunities to learn new prevention strategies, said Matt Stasiewicz, a professor of food science and human nutrition at the University of Illinois Urbana-Champaign. He discussed how such outbreaks happen and how they are traced and addressed in an interview with News Bureau biomedical sciences editor Liz Ahlberg Touchstone.
How do these multistate outbreaks happen?
For a multistate outbreak to happen, there must be a common source of a food distributed to multiple states where multiple people consume it. The food system is complex. That’s the thing a lot of consumers don’t really appreciate. Let’s take the onions as an example: You can walk into a store and buy bags of onions or loose bulk onions. Food services that supply things to restaurants and other customers also can sell the onions chopped, slivered, diced, all these different options. Because of scale and efficiency, there is often one region in the U.S. that’s growing onions at any given time. So it might be all of those formats of onion are coming from a single region, processed at only a couple of facilities. That creates this centralization where it’s all being processed into multiple items. That’s why some recalls can include many items sold under different brand names.
How are the sources of outbreaks investigated and identified?
We identify the outbreak when multiple people get sick and then interact with the health system — usually, by going to their doctor. Samples are taken and if a pathogen is found, its whole genome is sequenced. Those results go into a big national database that the Centers for Disease Control and Prevention can monitor. When there’s a cluster of illnesses caused by a particular strain, that will trigger follow up.
Local public health agents will interview the people that were sick as a cluster and ask them what they ate. They’ll often then try to interview people of a similar demographic who aren’t sick to figure out what they ate. With luck, something will pop up to suggest a food that was more likely to be consumed by the people who got sick than the ones who didn’t. Once you get to a suspect food, you start talking to company that made or served the food to trace it back to their supplier.
In this recent E. coli outbreak, what popped up was a particular menu item from a large fast-food company, which was eventually narrowed to just one ingredient.
The other way that identification can happen is in the process of randomly checking foods in the food supply. Many state departments of health will randomly pull various foods known to be at risk of foodborne pathogens from shelves and test them. If they find a pathogen in the food, that gets sequenced to add to the database. Then if that sequence matches a cluster of people who become ill, you can link the food to the illness.
Once the source of a pathogen is identified, how is it addressed?
The big concept with an outbreak like this is understanding how the food system is adapting to prevent harm from this outbreak. And then there’s this broader question of, how do we improve the food system so that we learn from a from an event?
This latest E. coli outbreak was a good example of the system starting out a bit cautious. Once they identified a suspect hamburger item, the stores in affected areas stopped serving that item. First, stop the harm.
As investigators received more information, they identified that the likely source of the bacteria was the onions. Then the distributor of the onions notified the restaurant chain and other customers not to serve them. The onions were sold through food service, rather than directly to consumers, so that’s good. It’s a smaller number of people and businesses to notify, so that provided a nice way to rapidly remove the product from the food supply.
Once the contaminated food is excluded, lots of smart people — working in academia, in industry, in the supply chain — will attempt to figure out what ultimately went wrong, even if it’s just bad luck, so we keep improving safety over time. And that’s where the food industry is now and will be for the near future: What can we learn about how this contamination happened, so that in the future we can keep reducing the risk?
What can companies to do prevent contamination in their products?
Part of the challenge is that food is produced mostly outside, in open systems that are in nature, so we’re never going to get to a food system with zero risk of contamination. People are working on both preventing contamination and processing methods that reduce it.
In the produce space, one of the big things that the industry is working on right now is trying to understand the sources of environmental contamination. Water can be a risk. Animals of various sources can be risks. Pathogenic E. coli comes from mammalian intestines, so keeping wild animals out of produce fields and looking at proximity to large animal operations are areas of concern.
Some ways of washing and processing can reduce some pathogens as well. For example, the “triple washed” clam shells of leafy greens that you can get at grocery stores. That triple wash process will often contain food safe acid washes, which is very similar to if you were to use something acidic like lemon juice or vinegar when washing your produce at home. Something similar happens at a large scale and actually can reduce some risk that way.
What some new innovations addressing food safety to prevent pathogen exposure?
A lot of what we work on is thinking about risk, thinking about better decision making, and thinking about how we can use modern computation. I think that the fundamental transition that we’re working on in food safety now is that we’re not going to find silver bullets. We’re not going to find the perfect thing that sterilizes every onion, so we need to come up with a menu of options and then find the practices that work best to get us gains. We can take machine learning, AI and genomics and really apply them practically in the food system.
One of the things that our group is working on here at Illinois is better ways to do risk modeling, to figure out the things that are most risky for pathogen transmission in fields. What are better ways to sample fields to find pathogens before harvest? Is it better to spend more money on testing pre-harvest, or better to wash or some other new practice?
What can people do to minimize their exposure risks? And what should someone do if they suspect they are infected with a foodborne pathogen?
The standard Food and Drug Administration advice for food safety is good: cook, clean, separate, chill. All of those things reduce your risk of foodborne illness. So for something like this, if you’re worried about raw onions, you can cook them, and cooking is a great way to reduce your risk of foodborne disease. The challenge is for lots of foods, people don’t want to cook them. Maybe you want to eat raw vegetables or greens. And in that case, you’re left with the basic food safety practices such as washing and preventing cross contamination.
If you suspect you get a foodborne disease associated with this outbreak or anything else, and you feel the need to get medical care to recover, see a doctor. A lot of foodborne disease classically produces symptoms such as diarrhea, vomiting, maybe fever. If the symptoms are managed well, most people will recover fine at home on their own. The most critical thing is, if your symptoms are more severe, get medical attention. Foodborne pathogens can result in serious harms and hospitalization, so evaluate yourself, how you’re feeling and whether you need care.