Thousands of ready-to-eat pasta products have been recalled in connection with an ongoing listeria outbreak that has killed four and touched major retailers including Walmart, Kroger and Trader Joe's.

An Oct. 9 notice from the Food and Drug Administration (FDA) listed thousands of pre-cooked pasta products made by Nate's Fine Foods as being linked to the outbreak. The items were later distributed to makers of ready-to-eat meals. FreshRealm, a distributor from which multiple foods have now been recalled, along with the FDA and other partnering agencies, found that Nate's products tested positive for the outbreak strain of listeria.

Nate's Fine Foods first initiated a voluntary recall of 245,000 pounds of pre-cooked pasta on Sept. 25, citing potential listeria monocytogenes contamination. A notice shared by the U.S. Department of Agriculture's (USDA) Food and Safety and Inspection Service (FSIS) at the time linked the pasta to ready-to-eat pasta meals sold at Walmart and Trader Joe's.

As health agencies continue to investigate, more grocery chains are issuing recalls of specific products, such as Sprouts' new Oct. 8 recall of ready-to-eat Smoked Mozzarella Pasta Salad.

The recalls are just the latest of a 15-state outbreak first announced in June. As of Sept. 25, there were 20 confirmed cases of listeria poisoning linked to the outbreak, the Centers for Disease Control and Prevention (CDC) reported. At least four people are dead, and nearly two dozen were hospitalized. In one case, a pregnant woman experienced fetal loss as a result of a related infection.