https://www.msn.com/en-us/foodanddri...-us/ar-AAwntsM

A 2013 analysis by CDC of food poisoning cases between 1998 and 2008 found that leafy vegetables — salads and the like — caused almost a quarter of all food poisonings. That was more than any other food product, including dairy and poultry. Leafy vegetables were also the second most common cause of food poisoning-related hospitalizations.

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Michele Jay-Russell, a food safety researcher at the University of California Davis who has investigated salad-related poisoning outbreaks in the past, said the raw vegetables that are the most common culprits are basically all salad greens, but especially the chopped and bagged kind. “We really haven’t seen kale and some of the other greens [with contamination] problems, at least not yet. And romaine is one of the most common lettuce products that are used in salads.”

The article goes on to talk about why, if you're interested.