A widening US cyclosporiasis outbreak has again put lettuce in the very unglamorous role of disease vehicle. More than 7,100 people in Michigan alone have been sickened, and the outbreak is likely tied to iceberg lettuce supplied by Taylor Farms, according to Wired.
The broader problem is not new. Leafy greens have repeatedly appeared in foodborne illness investigations, including a 2022 multistate E. coli outbreak tied to romaine on Wendy’s sandwiches, 173 norovirus cases linked to D.C. Cobb’s in Illinois, a 2021 BrightFarms recall of packaged greens after 31 Salmonella illnesses, and a 2019 E. coli outbreak involving 167 people who had eaten romaine from California’s Salinas Valley region. In 2020, Fresh Express salad kits were connected to more than 700 cyclospora cases.
The Centers for Disease Control and Prevention estimates that produce accounts for nearly half of reported foodborne illness cases, with leafy vegetables leading that category. Lettuce is not cursed. It is popular, fragile, wet, folded, widely distributed, and usually eaten without the one processing step that reliably kills pathogens: heat.
Scale turns one bad batch into a lot of bad meals
Lettuce is the second-most eaten vegetable in the United States after potatoes. It shows up in fast-food sandwiches, wraps, tacos, salad chains, grocery-store kits, and plain heads of iceberg in the produce aisle. That volume gives pathogens a broad delivery network if contamination enters the supply chain.
Bagged salads and spring mixes add another multiplier. They often combine several types of greens, which can come from different farms or regions. A contaminated ingredient can spread microbes across the whole bag. Once that product is packed at scale and shipped out, the problem can travel far beyond the field where it began.
How lettuce is grown can put pathogens on the leaves
A 2025 Cornell University study of E. coli outbreaks in romaine found that much of the contamination traced to untreated surface water used in overhead spray irrigation. That method puts water directly onto the part of the plant people eat.
Researchers noted that other irrigation systems can reduce that contact. Those systems would require equipment changes and downtime, which is exactly the kind of unsexy operational fix that tends to disappear behind cheerful packaging and salad-bar aesthetics.
The crop’s structure also works against it. Jeanne Marrazzo, chief executive of the Infectious Diseases Society of America, told Wired that many lettuce varieties have folds and crevices where small pathogens can lodge. That is great if your goal is crunch. It is less great if microbes are already present.
Raw leaves skip the kill step
Unlike many processed foods, lettuce usually does not go through heating, pasteurization, or freezing meant to kill pathogens. People eat it raw because cooked lettuce is, for most diners, a culinary surrender. That means any contaminant that survives farming, harvesting, processing, and washing may still be on the leaf at lunch.
Prewashing at processing plants does not guarantee a clean product. Microbes can stick to leaves. Cyclospora is especially annoying: the parasite has thick outer walls that make it resistant to many food sanitizers, according to experts cited by Wired. Experts said forceful washing with scrubbing is the best way to remove cyclospora.
Amira Roess, an epidemiologist at George Mason University, told Wired that poorly washed produce can carry whatever is sitting on the lettuce into the person who eats it. That is the mechanical reality behind the recurring outbreaks: high-volume raw food, grown in open systems, with plenty of places for pathogens to hide.
This story draws on original reporting from WIRED.
