Tuberculosis

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Basics

Description

Tuberculosis (TB) is an infectious disease with protean manifestations, causing significant global morbidity and mortality

Mechanism
  • Infectious droplet nuclei are inhaled through the respiratory tract
  • Bacteria are dispersed through coughing, sneezing, speaking, and singing
  • Primary TB/latent TB infection (LTBI):
    • Initial infection occurs when organisms enter the alveoli, become engulfed by macrophages, and spread via regional lymph nodes to the bloodstream
    • Patients are usually asymptomatic
    • 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 active TB
    • May progress to active TB (5–10%)
  • Reactivation TB:
    • LTBI becomes active TB
    • Systemic (15%) and pulmonary (85%) symptoms
  • TB has an incidence of 2.9 cases per 100,000 in the U.S.
  • 2016 had the lowest number of reported new cases
  • Out of the approximately 9,200 new cases reported, 67% were foreign born and 86% were HIV positive
  • TB is the leading cause of death in those with HIV worldwide
  • Still an estimated 10–15 million people are infected in the U.S. alone

Etiology

  • Infection with Mycobacterium tuberculosis, a slow-growing, aerobic, acid-fast bacillus resulting in disease
  • Humans are the only known reservoir
  • 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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Basics

Description

Tuberculosis (TB) is an infectious disease with protean manifestations, causing significant global morbidity and mortality

Mechanism
  • Infectious droplet nuclei are inhaled through the respiratory tract
  • Bacteria are dispersed through coughing, sneezing, speaking, and singing
  • Primary TB/latent TB infection (LTBI):
    • Initial infection occurs when organisms enter the alveoli, become engulfed by macrophages, and spread via regional lymph nodes to the bloodstream
    • Patients are usually asymptomatic
    • 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 active TB
    • May progress to active TB (5–10%)
  • Reactivation TB:
    • LTBI becomes active TB
    • Systemic (15%) and pulmonary (85%) symptoms
  • TB has an incidence of 2.9 cases per 100,000 in the U.S.
  • 2016 had the lowest number of reported new cases
  • Out of the approximately 9,200 new cases reported, 67% were foreign born and 86% were HIV positive
  • TB is the leading cause of death in those with HIV worldwide
  • Still an estimated 10–15 million people are infected in the U.S. alone

Etiology

  • Infection with Mycobacterium tuberculosis, a slow-growing, aerobic, acid-fast bacillus resulting in disease
  • Humans are the only known reservoir
  • 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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