One person died and 12 others were hospitalized because of a multi-state Listeria outbreak associated with salads packaged from a Dole processing facility in Springfield, Ohio, CBS News reported.

The Listeria outbreak has been under investigation since September 2015. It has affected people, including one pregnant woman, from six states: four in Michigan, four in New York, one in Indiana, one in New Jersey, one in Massachusetts and one in Pennsylvania. One person from Michigan died because of the infection, according to the Centers for Disease Control and Prevention.

Upon investigation, the Listeria isolates collected from the 12 hospitalized people were found to be highly related genetically.

It was not until this month that the source of the outbreak was traced to the Dole Springfield facility. The Ohio Department of Agriculture isolated Listeria from a pack of Dole brand Field Greens, and the isolate was genetically related to the previous isolates collected from the 12 patients.

Dole halted all production at said facility on Thursday and has pulled out its packaged salads from the market.  

The salads were sold under different brands aside from Dole, including President's Choice, Simple Truth, The Little Salad Bar, Marketside and Fresh Selections. The packages' manufacturing code begins with the letter "A," the CDC said in an advisory.

At this time, there is no reason to believe that salads packaged from Dole's other facilities are also infected with Listeria, the CDC said. People who have bought possibly infected salads are advised to throw it out and wash the area where it was stored. 

Listeria, or listeriosis, is a serious type of food poisoning. The symptoms include headache, loss of balance, confusion, stiff neck and convulsions. Some cases lead to death. People most at risk are pregnant women, infants, older adults and people with weakened immune systems, according to the CDC.