MESA COUNTY, Colo. (CBS4) – Students at Palisade High School were back in class on Monday after their school and others in the Mesa County Valley District 51 were closed. The schools were wiped clean after a virus caused a number of illnesses.

Palisade High School closed early Thursday after hundreds of students and staff reported feeling ill.

Palisade High School closed early Thursday after hundreds of students and staff reported feeling ill. (credit: CBS)

Mesa County Public Health believes norovirus is to blame for the sick students and staff. The primary symptoms are vomiting and diarrhea.

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Elementary and middle schools had an in service teacher day on Monday. They will open to students on Tuesday.

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The first to close, Palisade High, was more than two weeks ago on Nov. 14. In that time, the schools were disinfected.

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“Custodial crews have devoted many hours to disinfecting each and every building over the break. Let’s help make sure their hard work does not go to waste and keep each other healthy!” the school district stated on Sunday.