Pertussis (Whooping Cough)

Overview – Pertussis (Whooping Cough)

Pertussis, or whooping cough, is a highly contagious respiratory disease caused by Bordetella pertussis, affecting individuals of all ages but particularly severe in infants under 12 months. Despite widespread vaccination, pertussis continues to circulate due to waning immunity. It is characterised by paroxysmal coughing fits, often followed by a characteristic “whoop” on inspiration. This article outlines the pathogenesis, clinical features, diagnosis, and management of pertussis with a focus on high-yield details relevant to medical students and junior doctors.

Definition

Pertussis is a bacterial respiratory infection caused by Bordetella pertussis, resulting in prolonged, severe coughing spells. It remains life-threatening in unvaccinated infants.

Aetiology

  • Bordetella pertussis
    • Gram-negative coccobacillus
    • Strict human pathogen (no animal reservoir)

Pathogenesis

  • Transmission: Airborne respiratory droplets
  • Colonises trachea and bronchi → Produces toxins:
    • Pertussis toxin:
      • ↑ Mucous production → persistent, ineffective cough
    • Tracheal cytotoxin:
      • Inhibits ciliary movement → impaired clearance
    • Dermonecrotic toxin:
      • Vasoconstriction and local ischaemia

These toxins disrupt the respiratory epithelium, leading to inflammation and paroxysmal cough with post-tussive vomiting.

Clinical Features

Classical Disease Progression (3 Stages)

  1. Catarrhal Stage (1–2 weeks)
    • Mild cough, rhinorrhoea, low-grade fever
    • Highly contagious at this stage
  2. Paroxysmal Stage (2–6 weeks)
    • Severe paroxysms of coughing
    • Inspiratory “whoop” (not always present in infants)
    • Post-tussive vomiting
    • Cyanosis, apnoea, or exhaustion in young children
  3. Convalescent Stage (weeks to months)
    • Gradual resolution of symptoms
    • Cough may persist for weeks (“100-day cough”)

High-Risk Group

  • Infants <12 months → high risk of:
Pertussis (whooping cough) prevention
https://www.canada.ca/en/public-health/services/reports-publications/canada-communicable-disease-report-ccdr/monthly-issue/2018-44/issue-9-september-6-2018/article-1a-pertussis-whooping-cough-still-danger-infants-infographic.html

Investigations

Diagnosis is primarily clinical during the paroxysmal stage.

  • Nasopharyngeal swab for PCR: most rapid and sensitive
  • Culture (Bordet-Gengou agar):
    • Takes up to 2 weeks → often not practical
  • Serology: useful in later stages
  • CBC: may show lymphocytosis (unusual for bacterial infections)

Management

First-Line Treatment

  • Macrolide antibiotics:
    • Azithromycin (preferred in infants)
    • Clarithromycin or Erythromycin (alternative)
  • Antibiotics reduce transmission, but may not alter disease course if started late

Additional Strategies

  • Vaccination:
    • Ensure age-appropriate DTP boosters
    • Tdap booster for adolescents and adults
  • Post-exposure prophylaxis:
    • Azithromycin for close contacts, especially infants or pregnant women
  • Hospitalisation:
    • For infants <6 months or severe disease
    • Supportive care, oxygen, hydration

Complications

  • Apnoea and respiratory failure
  • Pneumonia (often from secondary infection)
  • Seizures
  • Encephalopathy
  • Rib fractures or hernias from forceful coughing
  • Death (most common in infants <6 months)

Differential Diagnosis

Summary – Pertussis (Whooping Cough)

Pertussis is a vaccine-preventable bacterial infection that remains a serious risk in infants and unvaccinated individuals. It presents with a catarrhal prodrome followed by severe paroxysmal coughing fits and post-tussive vomiting. Prompt antibiotic therapy helps reduce spread, and vaccination of close contacts is essential. For broader context, visit our Respiratory Overview page.

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