CHICAGO (CBS) — A dozen cases of highly contagious whooping cough have been reported at two high schools and a middle school in the northwest suburbs.

The Cook County Department of Public Health said the county appears to be on pace to have fewer, or about normal numbers of whooping cough cases this year. However, a total of 12 pertussis cases have been confirmed at John Hersey High School in Arlington Heights, Prospect High School in Mount Prospect, and Highcrest Middle School in Wilmette.

In all, there were 111 confirmed cases of whooping cough in Cook County through the end of October, which is about average for this time of year. The number of cases seen at the three schools is not unusual, because doctors normally see an increase in pertussis cases in winter.

“It’s very contagious, like a bad cold,” said Dr. Robert Feldman, an emergency room physician at Stroger Hospital.

As a result, Feldman said it’s important to prevent the spread of the disease.

“Very important for the kids to get vaccinated. The other things are good hand-washing. If someone is sick – especially a child – really best, if possible, to keep them home from school,” he said.

Pertussis vaccinations are recommended for all children at the ages of 2, 4, 6, and 15 months; and then a booster at 4 to 6 years old.