article_snippet.sent: (CNN)The listeria outbreak that prompted Blue Bell Creameries to recall Blue Bell Creameries entire product line dates to 2010, according to the Centers for Disease Control.
article_snippet.sent: (Blue Bell) decided to yank all (Blue Bell) products after tests showed some half-gallon containers of chocolate chip cookie dough ice cream contained listeria.
article_snippet.sent: This means (Blue Bell) has now had several positive tests for Listeria in different places and plants," (Blue Bell) said in a written statement.
article_snippet.sent: At this point, we cannot say with certainty how Listeria was introduced to we facilities, and so we have taken this unprecedented step," (Blue Bell) said.
article_snippet.sent: Listeria didn't get into ice cream through the milk because (Blue Bell) uses pasteurized milk, Caroline Smith DeWaal, director of food safety for Center for Science in the Public Interest, told CNN on Tuesday.
article_snippet.sent: But Listeria could have been carried on foods like nuts that go into ice cream, Caroline Smith DeWaal said.
article_snippet.sent: DeWaal said the listeria probably wasn't linked to (Blue Bell) in 2010 because one case wouldn't spark a full investigation.
article_snippet.sent: Other culprits, such as cheeses and deli meats, would be considered before ice cream products, because listeria can't grow in frozen temperatures, Caroline Smith DeWaal said.
article_snippet.sent: Tests of those listeria strains "were nearly identical to Listeria strains isolated from ice cream produced at the Blue Bell Creameries' Oklahoma facility," the CDC said.