This time of year marks the beginning of the season for norovirus, one of the most infectious viruses known.

Classes in an entire school district in Colorado have been canceled Thursday and Friday after a suspected outbreak of the highly contagious norovirus.  In recent days, hundreds of students and staff in Mesa County Valley School District 51 have been complaining of an illness that comes on “incredibly fast” and leads to vomiting and diarrhea.

The problems started last week when about 30% of students and 20% of staff called in sick at a high school, said Emily Shockley, a spokeswoman for the district.

Credit: CDC

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