Americans are avoiding romaine lettuce after an outbreak - and it reveals one of the most dangerous grocery store habits

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Pre-packaged salad sits on the shelf at a Bell Market grocery store

• The CDC recommended on Friday that Americans avoid all forms of romaine lettuce.
• At least 53 people have been infected with E. coli after consuming romaine from the Yuma, Arizona region.
• Leafy greens - specifically those sold pre-washed - are one of riskiest foods when it comes to food poisoning.

A CDC investigation is putting leafy greens under the microscope.

On Friday, the Centers for Disease Control and Prevention recommended that Americans avoid any form of romaine lettuce. According to the CDC, at least 53 people in 16 US states have been infected with E. coli after consuming romaine lettuce from the Yuma, Arizona region.

Originally, the CDC only told shoppers to avoid pre-chopped lettuce, but expanded the warning to all types of romaine.

In this case, Americans have been instructed to avoid all types of romaine - including pre-chopped, whole heads, and hearts. However, the incident highlights a common shopping choice that increases the risk of food poisoning.

Pre-cut fruits and vegetables, such as salads in a bag, are extremely convenient. However, they also carry a higher risk of food poisoning, according to experts.

The process of washing, cutting. and bagging food increases the likelihood that it will become tainted, according to food poisoning attorney Bill Marler. According to Marler, he avoids pre-cut and pre-washed fruit and vegetables "like the plague."

A 2010 study from Consumer Reports found "unacceptable" levels of bacteria that commonly cause food poisoning in about a third of the 208 salad bags tested. As Business Insider's Rebecca Harrington notes, that doesn't mean these bacteria actually caused an illness- just that they had the potential to do so.

In general, leafy greens are one of the more dangerous food when it comes to food poisoning risks.

"A Centers for Disease Control and Prevention study found that from 1998 to 2008, leafy greens were associated with more incidents of food poisoning than any other single food category (though contaminated poultry led to more deaths)," Harrington reports.