Listeria monocytogenes is caused by a bacteria and can cause life-threatening illness. It is particularly dangerous for children, the elderly and pregnant women, in whom it can cause miscarriage.
A total of 83 percent of those interviewed so far (15 of 18 people) said they had recently eaten caramel-coated apples.
The US Centres for Disease Control and Prevention urged consumers in the United States not to eat commercially produced, prepackaged caramel apples until further notice.
Of the 28 infected, 26 were hospitalised and five people died.
"Listeriosis contributed to at least four of these deaths," said the CDC.
Nine of the cases were pregnancy-related and involved either mothers-to-be or their newborn infants.
Three cases of meningitis -- a dangerous complication of listeriosis -- among otherwise healthy children aged five to 15 were also reported.
Listeria can cause fever, muscle aches, nausea and diarrhea, and symptoms typically begin within a few days to a couple of months after eating a contaminated product.
The bacteria is found in soil, water and animal feces.
Listeria can infect raw vegetables, animal meat, unpasteurised milk and processed foods such as cheese dips and deli meats.
