ANN ARBOR, Mich. -

Local 4 has learned an outbreak of pertussis -- better known as whooping cough -- is getting worse in the Ann Arbor school district.

Washtenaw County health officials say 25 students have confirmed cases of whooping cough. They are all students at either Pioneer High School, Slauson Middle School or Skyline High School.

"We're not sure sure how many kids may have it but have not been tested," said Liz Margolis, of Ann Arbor schools.

Health officials say the students are being treated and all are expected to make a full recovery.

"It's airborne so we are clean at our schools, but because it's airborne any kind of close contact it can spread pretty fast," said Margolis.

Symptoms of whooping cough include coughs that come in bursts, vomiting after coughing spells and a cough that lasts a week or more.

Read more: Whooping cough outbreak hits Pioneer High School