After an incubation period of 7-10 days, a prolonged coughing illness begins. Symptoms are usually more severe in infants and young children.
- The initial symptoms (the catarrhal phase) are similar to those of the common cold (e.g., coryza, lacrimation, mild cough, low-grade fever, malaise) and last 1-2 weeks.
- The paroxysmal phase follows and lasts 2-4 weeks. It is characterized by a hallmark cough that occurs in spasmodic fits of 5-10 coughs each. Vomiting or a “whoop” may follow a coughing fit. Apnea and cyanosis can occur during spasms. Most complications occur during this phase.
- During the subsequent convalescent phase, coughing episodes resolve gradually over 1-3 months. For 6-12 months, viral infections may induce a recrudescence of paroxysmal cough.
- Disease manifestations are often atypical in adolescents and adults, with paroxysmal cough and the “whoop” being less common. Post-tussive emesis is the best predictor of pertussis as the cause of prolonged cough in adults.
- Lymphocytosis (an absolute lymphocyte count of >105/µL) suggests pertussis in young children, but is not common among affected adolescents and adults.