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.

Recalled supplemental shakes were distributed to hospitals and long-term care facilities nationwide, federal officials say.

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.