Diptheria

Potentially fatal contagious bacterial infection that mainly affects the nose and throat

Aetiology

  • Caused by Corynebacterium diphtheriae (gram-positive bacillus)
  • Transmitted via respiratory droplets or direct contact with skin lesions
  • Incubation period: 2-5 days
  • Rare in developed countries due to widespread vaccination
  • Still endemic in some regions with low vaccination coverage

Pathophysiology

  • The organism colonizes the respiratory tract mucosa
  • Produces a potent exotoxin (diphtheria toxin) that inhibits protein synthesis
  • The toxin has systemic effects:
    • Cardiotoxic: causes myocarditis and heart failure
    • Neurotoxic: causes demyelination leading to peripheral neuropathy
  • Local inflammation leads to formation of a pseudomembrane (grey-white membrane composed of dead epithelial cells, fibrin, bacteria, and inflammatory cells)
  • The pseudomembrane adheres tightly to underlying tissue and bleeds if removed

Clinical presentation

Local manifestations

  • Severe sore throat
  • Grey-white pseudomembrane across the pharynx, tonsils, or larynx
  • The membrane is firmly adherent and bleeds when removal is attempted
  • Bull neck appearance: massive cervical lymphadenopathy with neck swelling
  • Low-grade fever
  • Nasal discharge (in nasal diphtheria)
  • Hoarseness and stridor (in laryngeal involvement)

Systemic manifestations

  • Myocarditis: occurs in 10-25% of cases
    • Arrhythmias, heart failure
    • Usually appears 1-2 weeks after onset
  • Neuropathy: occurs in 75% of severe cases
    • Cranial nerve palsies (especially palatal paralysis)
    • Peripheral neuropathy (appears 3-7 weeks after onset)
    • Respiratory muscle paralysis
  • Acute tubular necrosis (renal involvement)
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Investigations

  • Throat swab: culture on selective media (Loeffler's or tellurite medium)
  • Gram stain: shows gram-positive bacilli with metachromatic granules
  • Toxin testing: confirms toxin production
  • ECG: monitor for cardiac complications
  • Serum antibody levels: assess immunity

Management

Acute management

  • Isolation of the patient (strict respiratory precautions)
  • Diphtheria antitoxin (DAT)
    • Administer as soon as possible (does not neutralize toxin already bound to tissues)
    • Dose: 20,000-120,000 units depending on severity and site
    • Horse serum-derived: check for hypersensitivity before administration
  • Antibiotics (to eradicate organism and prevent transmission)
    • Penicillin G or erythromycin for 14 days
    • Alternative: azithromycin or clarithromycin
  • Supportive care
    • Airway management (may require intubation or tracheostomy)
    • Cardiac monitoring (for myocarditis)
    • Bed rest (to reduce cardiac workload)

Prevention

  • Vaccination (most important)
    • Toxoid vaccine (inactivated diphtheria toxin)
    • Part of DTaP (children) or Tdap (adolescents/adults) vaccine
    • Primary series: 3 doses at 2, 4, and 6 months
    • Boosters: at 18 months, 4-6 years, then every 10 years
  • Post-exposure prophylaxis
    • Antibiotics (erythromycin or penicillin) for close contacts
    • Booster dose of vaccine for partially immunized contacts

Complications

  • Airway obstruction: from pseudomembrane extension
  • Myocarditis: leading cause of death (10-25% mortality)
  • Peripheral neuropathy: may take months to resolve
  • Acute renal failure
  • Septicemia
  • Death: mortality rate 5-10% overall, higher in young children and elderly