HOUSTON - City health officials were running tests Thursday night to determine what illness kept 328 elementary students home over two days.
Officials suspect a virus has caused the fevers, headaches and stomachaches that prompted Travis Elementary School students to miss class Wednesday and Thursday, the Houston Chronicle reported.
Health officials said they haven't ruled out environmental factors or even swine flu. They found no evidence of a food-borne illness.
Kathy Barton, spokeswoman for the city of Houston's health department, said seven students tested positive for Influenza A, a common form of the flu.
"We will be running a confirmatory test tonight in our lab," Barton told The Associated Press. "We'll know what's going on with those kids once we get the results."
It wasn't immediately clear how many students were sick.
"There were some that were held out of school for fear of them getting sick. We don't know what combination we are working with," Barton said.
She said the illness initially affected third-graders at the school but had spread to other grades and to employees. She did not know how many members of the staff were sick.
Children should remain at home until they have been fever-free for at least 24 hours, said Norm Uhl, a spokesman for the Houston Independent School District.