Stage	Duration(weeks)	Symptoms	Comment
Catarrhal	One to two	Lacrimation, low-grade fever, malaise, mild conjunctival inflammation, rhinorrhea, late-phase nonproductive cough	Insidious onset Gradually worsening symptoms
Paroxysmal	One to six	Paroxysms (bursts of coughing during a single exhalation) followed by an inspiratory “whooping” sound, post-tussive cyanosis, and emesis	Peaks after two weeks Weight loss, leukocytosis, and lymphocytosis are common
Paroxysmal	One to six	In infants younger than six months (especially those younger than four weeks): apnea, bradycardia, prolonged cough, poor feeding, no paroxysms
Convalescent	Two to 12	Paroxysms gradually improve but recur with respiratory infections	White blood cell count normalizes