The U.S. Food and Drug Administration (FDA) is working together with the Centers for Disease Control and Prevention (CDC) in collaboration with state and local partners to investigate illnesses in a multi-state outbreak of Listeria monocytogenes infections.

A listeria outbreak linked to frozen nutritional milkshakes is to blame for 12 deaths and dozens of hospitalizations, the U.S. Food and Drug Administration confirmed Monday following an investigation that spanned years.