Pertussis unfolds in three phases:
Catarrhal (1–2 weeks) – mild runny nose and low-grade fever; most contagious.
Paroxysmal (2–6 weeks) – clusters of 10–20 rapid coughs ending in an audible
“whoop” on inspiration, often followed by vomiting.
Convalescent (2–6 weeks) – cough gradually subsides but may re-emerge with
future respiratory infections.
Adults may lack the classic whoop yet can still transmit the disease.