A dozen cases of whooping cough — known as pertussis — have been reported on Bainbridge Island within the past three months, according to the Kitsap Public Health District.

Health officials said the number of cases of whooping cough have been rising, with 34 cases of pertussis reported in Kitsap County since July.

Officials with the Bainbridge Island School District sent a letter to parents Wednesday from the health district that encouraged parents to have their children immunized against the bacterial infection, and to seek a medical evaluation if symptoms of whooping cough were found.

Signs of whooping cough include a runny nose, slight cough and mild fever, and coughing episodes that gradually worsen over one to two weeks. The coughing episodes can include gagging and vomiting, loss of breath and difficulty with breathing.