CHICAGO (CBS)– A northwest suburban middle school is reminding parents to keep their kids home if they’re sick, and urging students to wash their hands, after nearly 200 students called out sick on Wednesday.

Officials at South Middle School in Arlington Heights confirmed 185 students called out sick with a potential flu virus on Wednesday; more than 20 percent of the school’s overall student population of 884 kids.

Parents who dropped off their kids for school on Thursday said they’re concerned about the number of flu cases.

“The school is a big petri dish, and if one kid comes to school sick, it kind of just snowballs. I think the important thing is that the parents learn that, as much as it’s convenient to send your kid to school, because of whatever arrangement you have at home, it’s more important to keep them home to get well, and not infect other kids,” parent Robert Smith said.

A school spokesperson said, in the past week, parents of 31 students reported verified cases of Influenza A.

The school sent letters and emails to parents this week, after 158 students called in sick on Tuesday, and 185 called in sick on Wednesday.

“Our custodial team is treating some areas of the building more frequently to help prevent the spread of germs,” the letter stated. “Several of our teachers had students using their school supplies wipes to address personal items and surfaces around them in the classroom/lockers.”

The letter also encouraged students to wash their hands and use hand sanitizer, and asked parents to help control the spread of viruses at home by cleaning and disinfecting high-touch surfaces.

“My daughter’s been sick a lot for other things, but now she’s fine. So she thought she brought the flu in, but it’s the way things go, I guess,” parent Greg Dittmer said.

South Middle School officials said they also are consulting Cook County Health Department guidelines to help control the spread of illness.