The elusive cause of an E. coli outbreak that has sickened 109 people across six states is being traced to ground beef, the Centers for Disease Control and Prevention said Friday.

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Update 5:35 p.m. EDT April 12: Officials believe the outbreak is caused by not thoroughly preparing ground beef. No specific brand has been identified as the cause. Illnesses have been reported by 109 people in six states, officials said Friday.

“If preparing ground beef, cook thoroughly to kill germs and wash hands, kitchen surfaces with soap and water after touching raw meat,” officials said.

Original report:

An E. coli outbreak has sickened 72 people across five states and the cause is eluding health officials, the Centers for Disease Control and Prevention said Friday.

People started becoming sick March 2, with cases reported in Georgia (eight), Kentucky (36), Ohio (five), Tennessee (21), and Virginia (two), according to the CDC. Eight people were hospitalized. No deaths have been reported.

There is no specific food item, grocery store or restaurant chain identified as the source of the infections, officials said.

"This is a rapidly evolving investigation," the CDC said in a release. "We will update our advice if a source is identified."