SHELBY, N.C. -- The number of people sickened in the E. coli outbreak continued to grow Friday.
State health officials confirmed there are now 15 cases in Cleveland, Gaston and Lincoln counties.
Of the people infected with the E. coli virus, 10 are children. Authorities say at this point in the investigation, there doesn't seem to be any common denominator in the cases, except they all attended the Cleveland County fair.
"We are checking everything, but right now it is a mystery," said Cleveland County Health Director Dorthea Wyant. “Nothing seems to stand out as the reason."
Wyant tells NBC Charlotte the department is conducting surveys with people who didn't get sick, as well as those sickened, to see if there is something everyone did.
"At this time, only a handful of people ate the same thing or visited a petting zoo. There isn't enough to link any one thing to the virus," said Wyant.
She noted another theory that rain may have washed animal feces into the soil of walkways used by the public.
The State Health Department did take samples, but Wyant said results will likely be inconclusive.
The symptoms of E. coli can vary but can include stomach cramps, vomiting and bloody diarrhea. It can take several days for symptoms to show.