The Cole County Health Department has identified the illness that sickened nearly 100 students last week.
The health department said norovirus is to blame for sickening students at the Cole County R-1 Elementary and Middle School.
Officials determined the sickness based on the students' symptoms, duration of sickness and test results from the Missouri State Public Health Laboratory.
Health officials say norovirus is a viral infection and causes vomiting, diarrhea, nausea and stomach cramping. Symptoms typically last for one-to-two days.
The health department is urging everyone to use proper hand-washing techniques since there is no vaccine or treatment for the virus.