(CBS) – The flu virus has shuttered another school in our area: Komarek Elementary School in North Riverside.

Even after a thorough cleaning over the weekend, they still had 30 additional kids sick on Monday, CBS 2’s Roseanne Tellez reports.

School officials announced the building would be closed for the rest of the week. On Tuesday, cleaning crews were parked outside, and masked workers could be seen disinfecting inside.

“We can’t let our kids and staff come into the building that we know is just not safe,” Supt. Brian Ganan says.

A letter to parents posted on the district website apologized, saying the closure “may be an inconvenience but this year’s flu is extremely contagious and dangerous.”

Ganan says 25 percent of 550 students were absent Monday, or forced to leave early due to the flu.

“I was in the nurse’s office yesterday, and I have never ever seen that kind of traffic,” he says. “It was nonstop. Our nurse did a phenomenal job.”