Etiology and pathophysiology : Tuberculosis

Etiology and pathophysiology

  • Spread via airborne particles
  • Can be suspended in air for minutes to hours
  • Transmission requires close, frequent, or prolonged exposure
  • NOT spread by touching, sharing food utensils, kissing, or other physical contact
  • Once causative organisms gains entrance, particles lodge in bronchioles and alveoli
  • Local inflammatory reaction occurs
    • Ghon lesion or focus – represents a calcified TB granuloma
    • Infection walled off and further spread stopped
  • Only 5% to 10% will develop active TB
  • Aerophilic (oxygen-loving) – causes affinity for lungs
  • Infection can spread via lymphatics and grow in other organs as well
    • Cerebral cortex
    • Spine
    • Epiphyses of the bone
    • Adrenal glands


  • Classes
    • 0 = No TB exposure
      • No TB exposure, not infected (no history of exposure, negative tuberculin skin test)
    • 1 = Exposure, no infection
      • TB exposure, no evidence of infection (history of exposure, negative tuberculin skin test)
    • 2 = Latent TB, no disease
      • TB infection without disease (significant reaction to tuberculin skin test, negative bacteriologic studies, no x-ray findings compatible with TB, no clinical evidence of TB
    • 3 = TB, clinically active
      • TB infection with clinically active disease (positive bacteriologic studies or both a significant reaction to tuberculin skin test and clinical or x-ray evidence of current disease)
    • 4 = TB, not clinically active
      • No current disease (history of previous episode of TB or abnormal, stable x-ray findings in a person with a significant reaction to tuberculin skin test. Negative bacteriologic studies if done. No clinical or x-ray evidence of current disease)
    • 5 = TB suspected
      • TB suspect (diagnosis pending). Individual should not be in this classification for >3 months
  • Primary  infection
    • When bacteria are isoniazidaled
  • Latent TB infection (LTBI)
    • Infected but no active disease
  • Active TB disease
    • Primary TB
    • Reactivation TB (post-primary)


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