SPRINGFIELD, Minn. (WCCO) – The illness that made 30 Springfield Public School students sick enough to go to the hospital Thursday was not caused by carbon monoxide, according to the Minnesota Department of Health.

A group of fourth and fifth graders became sick while rehearsing for a choir concert. On Friday, school officials say all the students are fine, and health officials think the illness may have been caused by nerves.

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Bethany Mattson says she was never really worried about her fifth-grade daughter, who was rehearsing with her classmates Thursday morning in the school’s auditorium. But she can see why other parents may have felt differently.

“She was in the auditorium but she was not sick,” Mattson said. “Kids just started fainting, and then some needed to go sit down because they didn’t feel good.”

As many as 30 fourth and fifth graders became sick, telling teachers they felt nauseous and had headaches. These are symptoms of carbon monoxide poisoning.

The school was evacuated and the students were taken to a clinic. Thirteen were tested for carbon monoxide, and each test came back negative.

Superintendent Keith Kottke says firefighters found no traces of anything in the school.

“[They] did their readings for carbon monoxide, carbon dioxide, appropriate oxygen levels and violate chemical,” Kottke said. “And we have found nothing.”

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Food poisoning was also ruled out. With the evidence at hand, state health officials believe anxiety may be to blame. It’s a unique theory they refer to as “mass psychogenic illness.”

It’s a phenomenon that can happen in groups of children; one child gets sick and throws up, and those symptoms quickly spread to other kids.

State health officials say the Springfield case would be a classic scenario.

“I’ll leave that theory to them,” Kottke said. “That’s beyond the scope of my education.”

Classes and basketball games were canceled Friday, and seven carbon monoxide detectors were installed as a precaution.

But Superintendent Kottke says school will resume as normal on Monday morning.

“We’re going to just continue to be vigilant and do our due diligence in making sure there isn’t something that we have missed,” he said.

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Kottke says they will check emissions at bus pickups and dropoffs on Monday morning. The school hasn’t decided if students will have to make up Thursday’s missed day.

John Lauritsen