Diphtheria

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management

Definition

Diphtheria is a highly contagious bacterial infection caused by Corynebacterium diphtheriae, primarily affecting the respiratory tract and producing a toxin that can lead to systemic complications.

Aetiology

• Caused by Corynebacterium diphtheriae, a Gram-positive bacillus.
• Spread via respiratory droplets, direct contact, or contaminated surfaces.
• Produces diphtheria toxin, which inhibits protein synthesis, leading to cell necrosis.

Pathophysiology

• Bacteria colonise the pharynx, larynx, or nose, forming a pseudomembrane.
• Diphtheria toxin is absorbed into the bloodstream, causing systemic effects.
• Toxin-mediated complications include myocarditis, neuritis, and acute renal failure.

Risk Factors

• Incomplete or absent diphtheria vaccination.
• Close contact with an infected individual.
• Overcrowded or poor sanitary conditions.
• Travel to endemic areas.

Signs and Symptoms

• Respiratory diphtheria:
  • Sore throat and fever.
  • Thick, greyish pseudomembrane over the tonsils, pharynx, or larynx.
  • Stridor, hoarseness, or respiratory distress.
  • Cervical lymphadenopathy ("bull neck").
• Systemic complications:
  • Myocarditis (arrhythmias, heart failure).
  • Neuropathy (cranial nerve palsies, paralysis).
  • Acute kidney injury.

Investigations

• Throat swab culture: confirms C. diphtheriae infection.
• Toxin assay (Elek test or PCR): detects diphtheria toxin.
• ECG: assess for myocarditis.
• Blood tests: check inflammatory markers and renal function.

Management

1. Isolation and Infection Control:

• Respiratory droplet and contact precautions.
• Notify public health authorities.

2. Antitoxin Therapy:

• Diphtheria antitoxin (DAT) to neutralise circulating toxin.
• Administer after sensitivity testing to avoid allergic reactions.

3. Antibiotic Therapy:

• First line: erythromycin or penicillin for 14 days.
• Alternative: clarithromycin or azithromycin if allergic.

4. Supportive Care:

• Airway management if obstruction occurs.
• Cardiac monitoring for myocarditis.
• IV fluids and electrolyte correction.

5. Prevention:

• Routine diphtheria vaccination (DTaP, Td booster every 10 years).
• Post exposure prophylaxis for close contacts (antibiotics and booster vaccination).

6. Referral:

• Infectious diseases: for management of confirmed cases.
• Cardiology: if myocarditis develops.
• Intensive care: if respiratory failure occurs.

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