More cases of whooping cough have been found in Douglas County, the health department said Wednesday.

The county reported two additional cases of pertussis, or whooping cough, bringing the total to seven. The cases have mainly been found in elementary and preschool children.

The affected schools have been notified and letters sent home to families. Those in close contact with those infected have been urged to seek treatment.

The cough is highly contagious.

Symptoms often resemble a common cold, including runny nose, cough and low fever. The cough is often high pitched and can be followed by vomiting.

The infection is spread through close contact, such as the sharing of water bottles or eating utensils. Health officials recommend that people with symptoms contact a physician. A vaccine is available.