Tuberculosis

Basics

Description

  • Tuberculosis (TB) is an infectious disease with protean manifestations, causing significant global morbidity and mortality
  • Terminology (WHO 2022 Guidelines):
    • Tuberculosis infection: Evidence of immunologic response to Mycobacterium tuberculosis in the absence of signs or symptoms of disease (prior term latent tuberculosis)
    • Tuberculosis disease: Signs or symptoms reflecting active illness due to Mycobacterium tuberculosis (prior term active tuberculosis)

Mechanism

  • Infectious droplet nuclei are inhaled through the respiratory tract
  • Bacteria are dispersed through coughing, sneezing, speaking, and singing
  • Tuberculosis Infection:
    • Initial infection occurs when organisms enter the alveoli, become engulfed by macrophages, and spread via regional lymph nodes to the bloodstream
    • Evidence of cell-mediated immunologic response in the absence of symptoms of illness
    • May be progressive/fatal in immunocompromised hosts
    • Positive reaction to purified protein derivative (PPD) indicates past exposure or infection
    • Negative PPD does not rule out TB disease
    • May progress to TB disease depending on underlying conditions
  • Reactivation TB:
    • TB infection becomes TB disease
  • TB has an incidence of 2.5 cases per 100,000 in the US (CDC, 2024)
  • Out of the approximately 8300 new cases reported, 73% were foreign born and 4.3% were HIV positive
  • TB is the leading cause of death in those with HIV worldwide
  • Up to 13 million people are estimated to be living with TB in the US

Etiology

  • Infection with Mycobacterium tuberculosis, a slow-growing, aerobic, acid-fast bacillus resulting in disease
  • Humans are the only known reservoir
  • HIV infection is greatest risk factor for TB disease
  • Recent TB epidemics:
    • HIV-infected patients
    • Multidrug-resistant TB (MDR-TB)
    • Extensively drug-resistant TB (XDR-TB):
      • High mortality, few effective drugs

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