More than 55,000 pounds of frozen blueberries have been recalled due to a potentially fatal listeria monocytogenes contamination, according to a Food and Drug Administration update.

The Oregon Potato Company first issued a recall of its IQF Blueberries on Feb. 12, but the FDA on Tuesday upgraded that recall to a “Class I,” which, according to the agency, means there is a “reasonable probability that the use of or exposure to a violative product will cause serious adverse health consequences or death.”

The frozen fruits were sold in 30-pound cases and 1,400-pound totes and are packaged in polyethylene bags or liners within the totes.

These blueberries were not sold directly to consumers from retail stores but were distributed in Michigan, Oregon, Washington, Wisconsin and in Canada. The FDA did not specify where the blueberries were sold or how consumers may have come into contact with them.

The products were potentially contaminated with listeria monocytogenes, according to the FDA announcement.

The bacteria can be found in many places, according to the FDA, including soil, water, sewage, rotting vegetation and in animals. It can cause a disease called listeriosis if contaminated food is eaten.

There are two types of listeriosis. The less-severe version causes mild symptoms such as fever, muscle aches, nausea, vomiting and diarrhea, according to the FDA.

But the more-severe version is life-threatening, according to the FDA, and symptoms can include headache, stiff neck, confusion, loss of balance and convulsions. This type of infection is more serious for newborns, adults over 65 and those with weakened immune systems.