How Do Leafy Greens Get Contaminated With E. Coli?

You’ve seen the warnings, read the headlines. It seems like every few months or so, we hear of yet another E. coli outbreak or scare. Much of the time, it’s linked to lettuce, spinach or some other type of leafy green. In August of 2022, an E. coli outbreak was thought to be linked to Wendy’s lettuce. January of the same year saw another outbreak, this time believed to be caused by spinach. In the fall of 2020, yet another outbreak was linked simply to “leafy greens.” So, why are our salads so often responsible for food safety scares?

To understand why we keep seeing these kinds of outbreaks stemming from contaminated greens, we have to take a closer look at what E. coli is. E. coli is a variety of bacteria that’s usually found in animal (including human) intestines, but not all types of E. coli are harmful to humans. In fact, of the over 700 different kinds of E. coli, the vast majority won’t cause illness. Some result in mild abdominal upset or diarrhea. But other types of E. coli produce a toxin called Shiga, which can cause serious damage to our organs. This toxin attacks the intestines and kidneys, sometimes resulting in a disease called hemolytic uremic syndrome. HUS can be fatal, particularly for young children.

In years past, E. coli outbreaks were mostly attributed to ground beef products. When a cow is slaughtered, contaminants from the intestines can be spread throughout the animal’s flesh. In the case of ground beef, meat from many animals is typically mixed together. That means that if one cow is improperly slaughtered and contaminated with Shiga-producing E. coli bacteria, it can contaminate all the other meat it’s processed with. For years, the presence of dangerous E. coli in ground beef was just a given in the beef industry, but in the early ‘90s, when an E. coli outbreak linked to Jack in the Box hamburgers sickened over 700 people and killed four children, the USDA regulated the industry, declaring that beef could no longer contain any Shiga-producing E. coli bacteria at all.

If E. coli comes from animal intestines, though, why are we seeing it popping up more and more in leafy greens? The short answer: capitalism. The longer answer is a bit more complicated than that. Many cases of E. coli have been attributed to water contaminated by nearby CAFOs, or concentrated animal feeding operations, which is where the majority of our meat and dairy comes from. The animals’ fecal matter, which can contain Shiga-producing E. coli, finds its way into the irrigation systems of nearby vegetable farms and is then sprayed onto the crop. E. coli can be killed with cooking, but since lettuce and other leafy greens are very rarely cooked, that bacteria is never killed, as washing the produce can’t destroy E. coli. This isn’t how all leafy green E. coli outbreaks happen, but it’s a significant enough problem for Congress to introduce a bill that would give regulatory agencies permission to test CAFOs for E. coli and other animal pathogens.

This bill, if passed, could be a step in the right direction, but it doesn’t change the fact that large-scale, inhumane and environmentally destructive forms of meat production, like CAFOs, can have unintended—and dangerous—consequences. When the production of food becomes all about profit rather than actually feeding people, it’s unsurprising that people eventually fall ill, whether from pathogens like E. coli or from addictive foods spiked with ungodly amounts of sugar and salt.

It’s important to remember, though, that individual farmers aren’t always to blame—they are often under tremendous pressure just to make ends meet. Moving an entire CAFO or lettuce farm in response to fears of contamination is likely not economically viable for most producers, even if they wish they could. Rather, we should be pointing at the system that necessitates these unsafe, unhealthy practices in the first place. What if we didn’t have to cram animals into a meat production hellscape that treats them like products instead of living beings? What if major corporations hadn’t pushed most small farmers out of the industry and we could buy our produce from smaller-scale producers that we knew and trusted? What if producers didn’t have to put safety on the back burner to prioritize paying their bills? Perhaps the food safety landscape would look different than it does today.

Can we build a world in which healthy, affordable and accessible food can be enjoyed without fear of hunger or disease? I hope so. In the meantime, I’ll roll the dice for a well-dressed Caesar salad.

Samantha Maxwell is a food writer and editor based in Boston. Follow her on Twitter at @samseating.