New cases of whooping cough have been reported in both Cook and Lake counties, according to health officials.
Two high schools, one in Lincolnshire and one in Winnetka, have reported cases of the highly contagious disease this week.
The Archdiocese of Chicago has confirmed several whooping cough cases at the School of Saints Faith, Hope and Charity in Winnetka, where the student body totals 330.
The archdiocese sent a note Friday to alert parents.
According to health officials, there have been 44 confirmed cases of pertussis in suburban Cook County this year.
Lake County has seen double that amount, totaling 92 confirmed cases this year.
The Lake County Health Department has worked with three high schools in the area, including Stevenson High School in Lincolnshire. Stevenson had the most recent cases confirmed this week.
The cough starts mildly and then progresses to the point where symptoms can include vomiting.
Stevenson High School officials are trying to get the illness under control.
"It's really a matter of nurses trying to identify classic symptoms of pertussis," said Jim Conrey, the high school's public information coordinator.
A mass email sent to 11,000 parents, students and staff asks individuals to stay home if pertussis is suspected. The notice comes after one of the infected students attended the homecoming dance with 2,500 other students.
Whooping cough affects all ages.
According to the Lake County Health Department, a vaccination is the best way to prevent the illness.
If you catch the illness after receiving the vaccination, health officials said that symptoms will be less severe.
New cases of whooping cough reported in Cook, Lake counties