Humans get sick with listeria infections, or listeriosis, from eating soil-contaminated food, undercooked meat or dairy products that are raw or unpasteurized. Listeria can cause convulsions, coma, miscarriage and birth defects. And it's the third leading cause of food poisoning deaths in the U.S.
Avoiding unseen food hazards is the reason people often check the dates on food packaging. And printed with the month and year is often one of a dizzying array of phrases: "best by," "use by," "best if used before," "best if used by," "guaranteed fresh until," "freeze by" and even a "born on" label applied to some beer.
