A sweet treat popular around the holidays has put dozens of people at risk in multiple states including Utah.
At least four people have died after eating caramel apples that may have been infected with Listeria monocytogenes.
According to the Centers for Disease Control and Prevention, 28 people have become infected with the deadly bacterium in 10 different states.
Of the 28 people who have become ill, nine patients were pregnant.
Experts say pregnant women are 10 times more likely to get listeriosis after eating infected food.
The CDC says three of the patients were children who were otherwise healthy.
Symptoms of listeriosis infection include muscle aches, headache, stiff neck, confusion, loss of balance, fever and convulsions.
Typically, symptoms begin three to 70 days after eating the tainted food.
Officials say 15 of the 18 people who were interviewed about their illnesses remembered eating commercially produced, prepackaged caramel apples before they became sick.
Most of those who were ill saw their doctor in late October and November.
Investigators are still trying to determine which specific brands are involved. They are also trying to figure out the source of the infected apples.
In the meantime, the CDC is warning customers who may have purchased caramel apples with toppings like nuts, chocolate or sprinkles not to eat them until investigators figure out the source of the contamination.
There are about 1,600 cases of listeriosis reported in the United States every year.
This kind of infection kills about 260 people annually, according to the CDC.