Sticks poked into caramel apples release enough juice to make a nice, nourishing place for Listeria bacteria to grow, researchers reported Tuesday.
The finding could explain a caramel apple-linked Listeria outbreak linked that killed seven people and sickened at least 35 last month, NBC News reported.
"Caramel-coated apples are not a food on which Listeria monocytogenes should grow," said Kathleen Glass, of the University of Wisconsin-Madison, and colleagues.
But in their experiment, the researchers found that apples with sticks inserted did grow Listeria, even inside refrigerators, albeit more slowly, they wrote.
Listeria can kill the very young, very old and people with weakened immune systems, and can cause miscarriages and stillbirths.