The McHenry County Health Department has confirmed at least nine cases of pertussis, or whooping cough, in the last 30 days. All involve students at Cary Grove High School in Cary.
Last year, McHenry County had a total of nine cases of whooping cough and 51 cases in 2009.
Whooping cough is a contagious bacterial infection that is spread through coughing and sneezing.
