Leafy greens are widely associated with healthy diets, but they are also a recurring source of foodborne illness in the United States. A growing cyclosporiasis outbreak has reportedly sickened more than 7,100 people in Michigan, with iceberg lettuce supplied by Taylor Farms identified as the likely source.
The incident follows several outbreaks involving lettuce and packaged salads. Romaine served at Wendy’s was linked to a multistate E. coli outbreak in 2022, while an Illinois restaurant reported 173 norovirus cases. In 2021, BrightFarms recalled packaged greens after 31 salmonella infections. Romaine from California’s Salinas Valley was connected to 167 E. coli cases in 2019, and Fresh Express salad kits were associated with more than 700 cyclospora cases in 2020.
According to the Centers for Disease Control and Prevention, produce accounts for nearly half of reported foodborne illnesses, with leafy vegetables responsible for the largest share. Their prominence partly reflects consumption: Lettuce is the country’s second-most-eaten vegetable, behind potatoes, and is common in restaurants, fast-food meals, grocery stores, and ready-to-eat products.
Bagged salads may present additional challenges because they combine greens from multiple farms or regions. Contamination in one ingredient can spread throughout a package and then reach consumers across a broad distribution network.
Production methods also matter. A 2025 Cornell University study found that untreated surface water delivered through overhead irrigation contributed to E. coli contamination in romaine. Alternative irrigation systems could reduce contact with leaves but may require costly upgrades and operational interruptions.
Because lettuce is generally eaten raw, it lacks a pathogen-removing “kill step” such as heating or pasteurization. Its folds and crevices can shelter microbes, while some organisms resist sanitizers. Experts recommend washing greens thoroughly, though commercial prewashing and home rinsing may not remove every contaminant. These factors make prevention dependent on safeguards from farms to kitchens nationwide.