People should throw away any salad that came from the facility, the Centers for Disease Control and Prevention says.
The outbreak was last summer but consumers shouldn't take chances, CDC said.
"On January 21, 2016, Dole reported to CDC that it had stopped all production at the processing facility in Springfield, Ohio and is withdrawing all packaged salads currently on the market that were produced at this facility," CDC said.
The salads were sold under various brand names, including include Dole, Fresh Selections, Simple Truth, Marketside, The Little Salad Bar, and President's Choice. "These packaged salads can be identified by the letter "A" at the beginning of the manufacturing code found on the package,' CDC said.
"CDC recommends that consumers do not eat, restaurants do not serve, and retailers do not sell packaged salads produced at the Dole processing facility in Springfield, Ohio."
Related: Five Things to Know About Listeria
The 12 cases were reported starting last July. Likely many more people were made sick, but the 12 serious cases were hospitalized and samples show they were infected with genetically related germs.
"At this time, there is no evidence to suggest that packaged salads produced at other Dole processing facilities in the United States are linked to illness," the CDC said.
"Although the investigation began in September 2015, the source of these illnesses wasn't known until January 2016 when the laboratory result from the packaged salad collected in Ohio linked the illnesses to the Dole processing facility in Springfield, Ohio."
CDC estimates that listeria puts 1,600 people into the hospital each year and kills 260 of them. Most at risk are people with weakened immune systems, such as the elderly, very young children and pregnant women. Listeria can cause miscarriages and it can infect newborns.