Blue Bell Creameries believes the listeria found at its Oklahoma facility is likely linked to a non-sanitary room, though the company has not been able to pinpoint a single source for the contamination at its Texas plant, according to a report released Wednesday. The Texas-company submitted information about how it plans to correct the problems to the U.S. Food and Drug Administration, which inspected Blue Bell plants after the company’s ice cream was linked to listeria illnesses in four states and three deaths in Kansas. The documents, released by the FDA in response to an open records request by The Associated Press, also confirm that surface areas tested at an Alabama plant turned up the most serious form of listeria. No illnesses have been linked to products made at that facility. Blue Bell stopped production at its plant in Brenham and at facilities in Broken Arrow, Oklahoma and Alabama after issuing a national recall in April. The contaminated products have been found at the company’s Texas and Oklahoma plants.