Contaminated lettuce has been at the heart of this year’s largest U.S. outbreak of cyclosporiasis, an illness caused by the parasite cyclospora that leads to explosive diarrhea, vomiting and dehydration that lands people in the hospital.
But this isn’t the first time lettuce has been implicated in outbreaks of the disease. In 2018, an outbreak linked to salads from McDonald’s sickened more than 500 Americans across 16 states, federal data shows. Two years later, an outbreak tied to Fresh Express bagged salad affected more than 700 people and a 2022 outbreak was traced to Caesar salad kits.
And it’s not just cyclosporiasis we need to worry about with lettuce, which has also been tied to E. coli and Salmonella outbreaks.
So, why is lettuce such a common culprit of foodborne illness? Well, there are a couple of reasons. For one, we eat a lot of it. The average American consumes an average of 25 pounds of lettuce annually.
Secondly, lettuce is hard to wash, which can leave you susceptible to any hitchhiking bacteria or parasite. “If you don’t wash these products well, you’re going to end up ingesting whatever is on the lettuce,” Amira Roess, an epidemiologist at George Mason University, told WIRED.
Bacteria and parasites can hide deep in the crevices between lettuce leaves, and it doesn’t help that lettuce grows close to the soil, either.
The closer produce is to soil, the more likely it is to come into contact with contaminated water that can spread cyclospora widely.
Contaminated water is the likely source of most big outbreaks, including this one, experts told The New York Times last week.
“You’d have to have a lot of produce being irrigated with a lot of water that was contaminated by a lot of cyclospora to see this number of cases,” Keith Schneider, a professor of food safety at the University of Florida, said.
And because of lettuce leaves’ tough yet fragile exterior, the versatile produce can be harder to clean than smooth-skinned products.
Broken leaves are also a problem, Barbara Kowalcyk, director of the Institute of Food Safety and Nutrition Security at George Washington University, told TIME.
She explained “that’s how the bacteria gets inside.”
Relying on pre-washed lettuce is not necessarily safe, either. Pre-washing may not remove microbes clinging to the leaves, including cyclospora, the University of Connecticut Extension said.
Lastly, we eat lettuce raw on sandwiches and in salads. That’s a big part of the problem.
Heating produce potentially contaminated with cyclospora to a temperature of 158 degrees Fahrenheit is the only thing that kills the parasite.
Cooking can also be effective against some strains of Salmonella and E. coli, if done right.
Parsley and cilantro are reportedly also tied to cyclospora cases in North Carolina, according to the New York Post.
Herbs have a lot of the same problems lettuce does. We eat them raw, they grow close to the ground and they’re often tough to clean.
Consumption of these herbs is rising, too, the U.S. Food and Drug Administration points out.
“Because these herbs may commonly be consumed without washing or a ‘kill-step,’ such as cooking, there may be an increased risk of human illness if microbial hazards are present,” the agency warns.
But experts say eating anything that could be affected is likely not worth the risk, whether that’s lettuce or other produce tied to foodborne illness.
“People often laugh when they hear the phrase ‘explosive diarrhea,’ but for the individuals experiencing it, there’s nothing humorous about it,” Darin Detwiler, a professor emeritus at Northeastern University, told Serious Eats. “Behind every reported case is a person whose life has been unexpectedly interrupted simply because they ate food they believed was safe.”
