Late last year, an outbreak of Listeriosis traced to caramel apples killed seven people and caused one miscarriage, and hospitalized dozens of people. These treats are most popular during the fall, which is Halloween season and apple-harvesting season, which is why consumers might be understandably worried that it could happen again this year. Microbiologists have found one possible cause of the contamination: sticks.

Normally, you eat a caramel apple impaled on a stick. In this outbreak, it was clearly the apples that brought Listeria to the party, and not the caramel or the sticks, but researchers at the University of Wisconsin discovered that apples with sticks that are stored without refrigeration are the most likely to spread Listeria.

The Washington Post explains that the researchers speculate that piercing an apple with a stick causes juices from the inside of the contaminated fruit to pour to the outside. If the apple is immediately dipped in caramel or chocolate, there’s a nice space between along the apple skin for the bacteria to multiply. Since cold temperatures slow the growth of Listeria, the researchers found less of the bacteria on refrigerated apples.

They deliberately contaminated the apples to see how different preparation and storage methods would affect the bacterial contamination, so keep that in mind: if your own apples are thoroughly washed, you don’t have much to worry about. Keep these issues in mind when you or a family member are tempted by a commercially prepared caramel apple, though.

Unrefrigerated caramel apples may pose deadly listeria risk, study suggests [Washington Post]

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