More products sold at Kroger stores have been recalled as the Food and Drug Administration continues to investigate a multistate listeria outbreak.

The 15-state outbreak has sickened at least 20, killing four, since the Centers for Disease Control and Prevention and the FDA began investigating cases of listeria poisoning, or listeriosis, in June. The illnesses have been traced back to pastas used in ready-to-eat products at grocery stores like Walmart and Kroger nationwide, prompting a cascade of developing recalls.

Kroger, along with competing grocer Giant Eagle, has added yet another set of items to its growing recall list on Oct. 4 as the investigation continues.

Here's what to know about the latest products added to the recall list.

Two recalled pasta salads were sold at the Kroger Co. Family of Stores in Alaska, Alabama, Arkansas, Arizona, California, Colorado, Georgia, Idaho, Illinois, Indiana, Kansas, Kentucky, Louisiana, Michigan, Missouri, Mississippi, Montana, Nebraska, New Mexico, Nevada, Ohio, Oregon, South Carolina, Tennessee, Texas, Utah, Washington, and West Virginia.