Severe illness is more common in young children who have not been immunized. Older immunized children or adults with pertussis have milder symptoms. The diagnosis of pertussis should be considered for older children or adults with persistent coughs to ensure they do not pass the infection on to young children. Pertussis is primarily spread when infected people cough or sneeze, expelling droplets that contain Bordetella pertussis bacteria. Older siblings or adults who may be harboring the bacteria in their nose and throat can infect an infant.
Pertussis begins as a mild upper respiratory infection.
Initially, symptoms resemble those of a common cold, including sneezing, runny nose, low-grade fever and a mild cough. Within two weeks, the cough becomes more severe and is characterized by episodes of numerous rapid coughs followed by a crowing or high pitched whoop. A thick, clear mucus may be discharged. These episodes may recur for one to two months, and are more frequent at night. Young children who have not been immunized have the most severe symptoms.