Norovirus Suspected After More Than 800 Illinois High School Students Stay Home Sick on Same Day The local health department is investigating.

 -- After hundreds of students missed school on the same day at a St. Charles, Illinois, high school, the county health department is investigating whether the mass illness is due to norovirus.

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

"It's pretty apparent that this is out of the ordinary," he said.

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

Tom Schlueter, the communications coordinator for the Kane County Health Department, said it is investigating the outbreak and working with the school district to confirm the cause. 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," he 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 Centers for Disease Control and Prevention. Most norovirus outbreaks occur from November to April, often where people are in close proximity to one another, such as "day care centers, nursing homes, schools and cruise ships," according to the CDC. Norovirus is the leading cause of illness from food contamination in the United State. Symptoms generally last one to three days.