GAYLORD, Minn. (WCCO) — The Minnesota Department of Health is “99 percent sure” that a Norovirus outbreak is to blame for a number of students going home sick in Gaylord, Minn., according to the school’s principal.

On Wednesday, 178 students at Sibley East Elementary and Sibley East Junior High schools were reported absent. On Thursday, the number was 211 students. The two schools are in the same building and together house about 600 students.

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According to the elementary school principal, not all the absences indicate sick students. Some were kept home to avoid catching whatever illness was afflicting other students.

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The principal said the health department is still looking into the situation, and though they’re confident the outbreak was Norovirus, only lab test results will tell for sure.

The school underwent a thorough cleaning of every chair, desk and locker on Wednesday, according to the principal. The school’s gym floor, bleachers and buses are being cleaned today.

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No after school activities were cancelled, and school is set to go on as scheduled Friday.