Students at Paynesville Area Secondary Schools were sent home early Tuesday and won't come back Wednesday, after more than 30 students became sick in the building this week.
The St. Cloud Times reports a handful of students began feeling "woozy" during a choir concert at the school Monday night. Several of those students were sent to the hospital and were later released.
When classes resumed Tuesday, more students reported feeling sick. Some were sent to the hospital to be checked out, but all were released by Tuesday afternoon.
WCCO says representatives from the state Health Department and Department of Homeland Security were at the scene.
The cause of the illness remains unclear. A St. Cloud hazardous chemical and assessment teams found carbon monoxide levels to be normal Monday and Tuesday. KARE 11 reports CO readings typically reach 60 before people become sick. The reading at the school was only a four.
Patients at the hospital were treated for carbon monoxide poisoning and influenza. All results came back negative, according to the St. Cloud Times.
Paynesville Area Secondary School has grades six through 12.