These are less spontaneous than in typical respiratory infections. Infants younger than 6 months often vomit in association with the cough, which leads to dehydration. Hypoxia tends to be more severe than the child's clinical appearance suggests. A significant number 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 posttussive emesis.
On average, they wait a median of 3 weeks before seeking treatment. Hypoxia should be considered. Dehydration is common on presentation. Mild fever is common. Fever over 39 C is rare.