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.

The frozen shakes were served at hospitals and long-term care facilities, sickening 38 people and resulting in 11 deaths in 21 states, according to the FDA.

According to a CDC food safety alert, an outbreak of Listeria infections has affected 38 people across 21 states. Of those infected, 37 have been hospitalized, and 12 have died.