A case of pertussis, commonly known as whooping cough, has been diagnosed in a ninth grade student at Pennfield Middle School on Forty Foot Road in Hatfield. Other cases have been diagnosed over the last three weeks in students at Montgomery and Bridle Path Elementary Schools, both in Montgomery Township, and at North Penn High School.  An e-mail Pennfield Principal Barbara Galloway sent to parents Monday says, “Your child may have been exposed.”  The Montgomery County Health Department says parents should watch their children over the next two weeks for a runny nose and sudden, uncontrollable coughing spells.