Clinical Features

The clinical course of the illness is divided into three stages: catarrhal, paroxysmal and convalescent.

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.

Stage	Length	Clinical Features
Stage 1: Catarrhal	Usually 7-10 days; range of 4-21	Characterized by: Coryza Low-grade fever Mild, occasional cough (which gradually becomes more severe)
Stage 2: Paroxysmal	Usually lasts 1-6 weeks, but may persist for up to 10 weeks	Characterized by: Paroxysms of numerous, rapid coughs due to difficulty expelling thick mucus from the tracheobronchial tree. Long aspiratory effort accompanied by a high-pitched "whoop" at the end of the paroxysms Cyanosis Vomiting and exhaustion Paroxysmal attacks: Occur frequently at night, with an average of 15 attacks per 24 hours. Increase in frequency during the first 1-2 weeks, remain at the same frequency for 2-3 weeks, and then gradually decrease.
Stage 3: Convalescent	Usually 7-10 days; range of 4-21	Characterized by: Gradual recovery Less persistent, paroxysmal coughs that disappear in 2-3 weeks Paroxysms often recur with subsequent respiratory infections for many months after the onset of pertussis.

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