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HAVERTOWN, Pa. (CBS) — The principal of Haverford Middle School in Havertown is warning parents that their children may have been exposed to whooping cough at the school.

Daniel Horan, the school’s principal, sent an email to parents and guardians of children at Haverford Middle School, saying that students may have been exposed to a case of pertussis, better known as whooping cough.

“Sometimes a child can get sick with pertussis after being around someone with the illness. This is especially true when the child has not received all of his/her pertussis vaccinations,” Horan wrote in the email.

Pertussis, which is a highly contagious disease, is spread through the air when an infected person sneezes or coughs.

People who contract pertussis usually begin with cold symptoms and a cough, which then becomes worse over a week or two.

Horan says that if a child comes down with these symptoms, they should not be attending school until evaluated by their doctor.

The principal advises parents that if they have any questions, to contact the Pennsylvania Department of Health, their doctor or the school’s nurse.