Authorities have interviewed "people of interest" in a criminal investigation centering on candy that may have made 21 high school students sick, Clarksburg Police Chief John Walker said Thursday.

The Liberty High School students fell ill with flu-like symptoms Wednesday, apparently after eating chocolate-covered caramel bars that had been sold as a fundraiser at the Harrison County school.

The candy bars, identified as the Kathryn Beich brand, were also sold at Van Horn Elementary School. Health officials recommend any candy purchased from either location be returned to the schools.

Walker said investigators with the U.S. Food and Drug Administration are helping in the investigation, but lab tests on the candy will not be available for several days.

However, police believe the outbreak of illness is an isolated incident, he said.

"We've identified some people of interest," Walker said, "but we've not made any arrests."

Walker said interviews have been conducted in the presence of polygraph operators from the State Police.

Carl Friebel, superintendent of Harrison County schools, said there is nothing to suggest a broader problem with the Kathryn Beich brand.

"We think the candy was a vehicle, not the cause," he said.

About eight students in gym class came down with symptoms, such as nausea and vomiting. Later Wednesday morning, another dozen students complained of similar symptoms.

The students were taken to United Hospital Center in Clarksburg, where all were treated and released.

Walker said none seems to have suffered any lasting effects.

Some areas of the school were cleaned extensively, then cleared by health officials to reopen.

Friebel said classes were "very normal" Thursday, with no sign of concern from either the 625 students or their parents.

"They took it in stride," he said. "I had no calls."