Cheese recall classified as potentially deadly. See affected products.

Thousands of containers of cheese have been recalled from stores nationwide due to the risk of serious illness or even death.

The pecorino romano cheese products were sold in 20 states to distributors and retail locations, including Sam's Club. The cheese, produced by the Ambriola Company, could be contaminated with listeria, a bacterium that can cause serious illness in some people, said the U.S. Food and Drug Administration report. Routine testing uncovered contamination at Ambriola's processing plant in West Caldwell, New Jersey, before the initial recall on Nov. 25.

The FDA updated the status of the recall on Jan. 6, categorizing it as Class I, meaning there is a "reasonable probability" that the use of, or exposure to, the product could cause "serious adverse health consequences or death."

"We take food safety very seriously and immediately alerted stores and distributors to remove the affected products from shelves," Ambriola Company chief executive officer Phil Marfuggi said in a statement shared in an FDA notice. "We are working closely with the FDA and continuing to test our products and facilities to fully understand the situation."

Here's what to know about the recall.