Define Whooping Cough. Describe its pathogenesis, stages, investigations and management.

Definition

• Whooping cough (pertussis) is an acute, highly contagious bacterial respiratory infection caused by Bordetella pertussis, characterised by paroxysms of coughing followed by an inspiratory 'whoop'.
• It is most severe and dangerous in young unimmunised infants.

Pathogenesis

• Spread by respiratory droplets; the organism attaches to respiratory cilia and releases pertussis toxin and other toxins → mucosal damage and impaired clearance.
• This produces thick secretions and the paroxysmal cough.

Clinical Stages

• Catarrhal stage (1–2 weeks): coryza, mild cough, low fever — the most infectious phase.
• Paroxysmal stage (2–6 weeks): bursts of rapid coughs ending in a whoop, often with post-tussive vomiting, cyanosis and subconjunctival haemorrhage.
• Convalescent stage: gradual reduction over weeks ('the 100-day cough').

Investigations

• Marked absolute lymphocytosis on the blood count.
• Nasopharyngeal swab for culture or PCR confirms the diagnosis.

Management

• Macrolide antibiotics — azithromycin/erythromycin (reduce infectivity; most effective in the catarrhal stage).
• Supportive care — oxygen, gentle suction, nutrition/hydration, and monitoring for apnoea (admit young infants).
• Isolation and chemoprophylaxis of close contacts.

Complications & Prevention

• Complications — pneumonia (commonest cause of death), apnoea, seizures, encephalopathy, hernia.
• Prevention — DPT/pentavalent vaccine (and maternal Tdap); this is the key protective measure.

Diagnosis — Supporting Points

• A prolonged cough (> 2 weeks) with paroxysms, whoop or post-tussive vomiting in an under-/partially-immunised child is highly suggestive.
• Contact with a chronic cougher; marked lymphocytosis on CBC.