As many as 26 people were taken to hospitals in two towns after the evacuation at Madill (Okla.) Elementary School.
An Oklahoma elementary school was evacuated Wednesday and more than two dozen students were treated for lightheadedness and nausea caused by a source that remains unknown, school and health authorities said.
Madill Elementary School in Madill, in south-central Oklahoma about 20 miles from the Texas state line, was evacuated about 10 a.m. (11 a.m. ET) after several students and staff members reported feeling ill.
Twenty-five students and at least one staff member were taken to hospitals in Ardmore and Madill, NBC station KTEN of Denison, Texas, reported.
One student remained at a Madill hospital for dehydration, but all other patients had been released by late Wednesday afternoon.
Anxious parents were allowed to pick up their children after classes were canceled.
"I was scared to death about my daughter to see if she was OK or not," Christy Rangeo of Madill told KTEN.
Madill Public Schools Superintendent Jon Tuck said that investigators still hadn't determined the cause of the illnesses late Wednesday afternoon. The Madill Fire Department ruled out a gas leak or carbon monoxide poisoning.
All classes and activities in the Madill Public Schools were canceled for Thursday, when state health officials are expected to disinfect the campus for viruses.
"We're going to do everything we can do to find out what this is," Tuck said. "We're not going to let our students come back to this facility until we're sure it's safe. Until that point, we will not be having school at our elementary."
By Jennifer French of NBC station KTEN of Denison, Texas, and M. Alex Johnson of msnbc.com.
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