Minimal or no fever. Mild but increasing cough. The Paroxysmal stage follows, lasting about 1-8 wk. These are less spontaneous than in typical respiratory infections. Infants under 6 mo often vomit in association with the cough, which leads to dehydration.
Hypoxia tends to be more severe than the clinical appearance of the child suggests.
A significant number will present with cyanosis and apneic spells. Vaccinated adults usually only develop a prolonged bronchitis without a whoop. Unvaccinated adults are more likely to have whooping and post-tussive emesis. On average they wait a median of 3 wk before seeking treatment. Hypoxia should be considered.