The latest tests bring to 31 the number of people who tested positive with the contagious bacterial infection, state officials said.
That's up from 20 confirmed infections the day before.
Of the 31 people now determined to be infected with E. coli, 27 had been to the fair. Many visited the children's petting zoo or were exposed to animals elsewhere on the fairgrounds.
Lab results are pending on 72 other people who are sick with symptoms that might indicate an E. coli infection, according to the state's Department of Health and Human Services.
Most of those infected are from the Triangle, including 17 people in Wake County.
The outbreak is the most significant one in the state since more than 200 people fell ill with the infection in 2001 in Robeson County after consuming unpasteurized butter.
The highly contagious E. coli bacterium commonly lives inside animals and can be passed to humans by eating contaminated meat or through contact with manure, animals or contaminated surfaces.
Ordinarily, North Carolina has about four or five cases of E. coli infection per month.
In most cases, a person with E. coli may be ill with diarrhea for a few days followed by improvement. However, the risk of transmitting the infection may continue for up to three weeks.