Dozens of children from Prospect Elementary School got sick in early December after a holiday party at the school.
A report released on Saturday showed homemade butter was the probable culprit.
Holly Floyd Locklear, a retired teacher, has been making the butter for 30 years. He says all the tests performed at his farm came back negative for E. coli.
Thirty-two cases have been confirmed since Nov. 28.
Health officials have said the outbreak could be the largest in state history. In 1998, about 125 people in Cleveland County showed symptoms of E. coli infection after eating contaminated coleslaw from a restaurant.
Sixty to 80 students have not returned to the school since the outbreak began. Some have been out of school since Nov. 20.
Health officials are requiring the students to have two negative E. coli tests before they can return. About 30 pupils were cleared to return last week.
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