iStock/Thinkstock(ST. CHARLES, Ill.) — After hundreds of students missed school on the same day at an Illinois high school, the county health department is investigating whether the mass illness is an outbreak of norovirus.

At least 800 of the 2,500 students at St. Charles East High School in St. Charles, Illinois, were absent on Monday after students reported symptoms consistent with norovirus, spokesman for St. Charles Community Unit School District Jim Blaney said at a press conference Monday. Student athletes first reported symptoms over the weekend.

“It’s pretty apparent that this is out of the ordinary,” Blaney said during the news conference.

A special bleach-based solution that can kill norovirus is being used to clean the high school, which was closed on Tuesday, Blaney said.

A spokesman for the Kane County Health Department said they are investigating the outbreak and working with the school district to confirm the cause of the outbreak. He said the students will need to be tested.

“It has all the earmarks of norovirus, but the only way to confirm, in fact, that it is norovirus is for someone to go to the doctor,” Tom Schlueter, communications coordinator for the Kane County Health Department told ABC News.

Norovirus is often referred to as the “stomach flu” and is highly contagious. Symptoms of infection include frequent vomiting, diarrhea and nausea, according to the U.S. Centers for Disease Control and Prevention (CDC). Most norovirus outbreaks occur between November and April, often in locations where groups of people are in close proximity to each other such as “daycare centers, nursing homes, schools, and cruise ships,” according to the CDC. It is also the leading cause of illness from food contamination in the United State. Symptoms generally last between one and three days.

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