Last year, California-based grocery producer Braga Fresh voluntarily issued a precautionary recall of 12-ounce washed and ready-to-eat Marketside Broccoli Florets sold at more than 1,000 Walmart stores due to the possibility of Listeria monocytogenes contamination.

The U.S. Food and Drug Administration upgraded the classification of recalled broccoli sold at Walmart originally issued in December to its highest recall category, according to the agency’s updated report.

The recall announced in January involves contaminated broccoli sold in 20 states. Here's everything you need to know