Six of the cases involve children, and two children are being treated in intensive care. Two others were hospitalized and released.
Officials say they don't know what caused the outbreak.
"It's generally through improper hygiene habits and preparation of foods, but there can be instances where exposure to animals," said Sue Lynn, Wake County Human Services.
All of the patients live in Wake County but in different households. Wake County Human Services is working with the North Carolina Division of Public Health to pinpoint the source.
The health department says it does not expect final lab results until next week.
Health officials say although a cluster of E. coli cases is not uncommon, they need to know if there are additional cases.
"If someone does exhibit the symptoms, which [include] severe stomach cramps, diarrhea, those types of symptoms, fever, they do need to seek out medical help," Lynn said.
E. coli exposure comes from contaminated water or food and is most likely found in raw vegetables and under cooked beef.
Signs of illness usually begin three or four days after being exposed to the bacteria, but some people may become sick as soon as one day after exposure.
Symptoms include diarrhea, abdominal cramping, pain or tenderness and nausea and vomiting.
The NC Department of Agriculture says it has not been asked to get involved in the investigation.
The health department expects to have more information Wednesday.
For more information about E. coli, visit http://epi.publichealth.nc.gov/gcdc/ecoli.html.