Dole company officials were aware a salad plant was contaminated with Listeria for a year and a half before they closed the facility, and did so only after the U.S. and Canada traced a deadly outbreak back to the plant, Food Safety News reports. The Listeria outbreak hospitalized 33 people in 2015 and early 2016; four of those patients died. According to an inspection report, Dole swab-tested its Springfield salad plant in 2014 and found positive results for Listeria, but continued to ship salads to dozens of states as well as at least five Canadian provinces.