The Food and Drug Administration (FDA) has issued a new warning about thousands of recalled eggs sold at Costco (COST) stores due to potential contamination with salmonella, a bacterium that can cause serious infections.

Nearly a month after a five-state recall of eggs sold at Costco, the FDA now says consumption of the recalled eggs could "cause serious adverse health consequences or death."

FDA escalates Costco egg recall to Class I, its highest risk level, over salmonella concerns. Learn what Class I means, how recalls escalate, and what it means for you.