Clinical features

The incubation period is on average between 7–10 days (range 5–21 days) and the infectious period is for 21 days after the onset of symptoms (1).

Classic (severe) pertussis, as defined by the World Health Organization (WHO), consists of at least 21 days of cough illness with paroxysms, associated whoops or post-tussis vomiting, and culture confirmation (1).

Clinical course of pertussis can be divided into 3 phases (2):

• Catarrhal phase.
  • Pertussis has an insidious onset with symptoms similar to mild respiratory infection (coryza, low grade fever, mild, occasional cough which gradually becomes more pronounced and comes in bursts or short paroxyms).
  • Lasts for 7-10 days and progresses to the paroxysmal coughing stage.
• Paroxysmal phase.
  • During a paroxysm, each inspiration is followed by a rapid succession of expiratory hacking coughs.
  • Paroxysms of cough:
    • often lasts for two to three months ("one-hundred-day cough") (1)
    • 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 (2)
  • Spasms of coughing may be followed by an inspiratory whoop, particularly in older children, and the child may become cyanosed or apnoeic.
  • The child may vomit thick mucus or food after a paroxysm, and after a spasm the child may be exhausted.
• Convalescent phase.
  • There is gradual recovery.
  • Lasts for 2-6 weeks (but can persist for months) (1,2).

Between coughing spasms, the child is usually perfectly well which may obscure the diagnosis unless careful attention is paid to the history. There are no added chest sounds.

The paroxysms of coughing may result in rise in intrathoracic pressure and reduction in venous return to the heart. The increased capillary pressure may then result in capillary rupture, particularly around the eyes causing petechiae and sometimes bruises.

Paroxysms often recur with subsequent respiratory infections for many months after the onset of pertussis (2).

References:

• (1) Public Health England (PHE). Pertussis brief for healthcare professionals
• (2) Centers for Disease Control and Prevention (CDC) 2013. Pertussis (Whooping Cough)