Clinical Features

The clinical course of the illness is divided into three stages:

• Catarrhal
• Paroxysmal
• Convalescent

Symptoms of pertussis usually develop within 5 to 10 days after being exposed, but sometimes not for as long as 3 weeks. Pertussis has an insidious onset with catarrhal symptoms that are indistinguishable from those of minor respiratory tract infections. The cough, which is initially intermittent, becomes paroxysmal. In typical cases paroxysms terminate with inspiratory whoop and can be followed by posttussive vomiting.

Paroxysms of cough, which may occur more at night, usually increase in frequency and severity as the illness progresses and typically persist for 2 to 6 weeks or more. The illness can be milder and the characteristic "whoop" absent in children, adolescents, and adults who were previously vaccinated. After paroxysms subside, a nonparoxysmal cough can continue for 2 to 6 weeks or longer.

Unvaccinated or incompletely vaccinated infants younger than 12 months of age have the highest risk for severe and life-threatening complications and death. In infants, the cough may be minimal or absent, and apnea may be the only symptom. Despite increasing awareness and recognition of pertussis as a disease that affects adolescents and adults, pertussis is often overlooked in the differential diagnosis of cough illness in this population. Illness is generally less severe, and the typical “whoop” less frequently seen in adolescents and adults. It is important to educate parents to consider pertussis when their child has a cough, letting them know that it can be a severe illness, especially for infants, and they should seek immediate treatment.