The Centers for Disease Control and Prevention is recommending "out of an abundance of caution" that U.S. consumers avoid commercially packaged caramel apples, as some of them may have caused an outbreak of food poisoning that's linked to five deaths so far.

As of Dec. 18, an outbreak of the bacteria Listeria monocytogenes has contributed to at least four and possibly five deaths, and has sickened 28 people in 10 states, the CDC said in a notice on its website Friday. The agency has not confirmed the presence of listeria in caramel apples, but many of the people hospitalized have reported eating caramel apples before they got sick.

Listeriosis can cause fever, muscle aches, nausea and diarrhea. It can be particularly harmful or even fatal to children, the elderly and pregnant women. At least three of those recently affected are children.

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The CDC has not yet ordered a recall on any specific products.

A representative for the CDC told CNBC the agency is still investigating the outbreak with the Food and Drug Administration, and that it has no additional information on the probe aside from what it's posted online.