Additionally, romaine, iceberg, and other lettuce were found to cause 60.8 percent of leafy green outbreaks, accounting for up to 75.7 percent of foodborne illnesses linked to the commodity, as well as 70 percent of costs. Out of all leafy greens subtypes, 19.8 percent of STEC O157:H7 illnesses are associated with romaine, according to the present estimates, resulting in approximately 12,496 cases of illness and costing $324.64 million in the U.S. annually.

The researchers underline the impact of modeling choices on attribution values, and therefore, estimates. For example, the modeling decision of whether to include outbreaks tied to single foods or complex foods is important. Limiting estimates to only outbreaks that involve singular foods or ingredients reduces false attributions, but underestimates risks from foods typically found as ingredients in complex foods. The three attribution models chosen for the study represent different approaches to this problem, basing estimates on simple food outbreaks, complex food and other ingredients, and complex foods considering compound probability distributions, respectively. Other modeling choices that varied across the models were whether to weigh outbreaks by number of illnesses and whether to discount or omit older outbreaks. Overall, no attribution model is “perfect” or universally accurate, stress the authors.