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Source: Peloquin CA, Namdar R. Tuberculosis. In: DiPiro, JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM. Pharmacotherapy: A Pathophysiologic Approach. 8th ed. Accessed July 23, 2012.

  • TB

  • Communicable infectious disease
    • May produce silent, latent infection, as well as progressive, active disease.

  • Caused by Mycobacterium tuberculosis, a bacillus.
  • Transmitted by coughing or sneezing.

  • Primary infection initiated by alveolar implantation of M. tuberculosis in droplet nuclei small enough (1–5 mm) to escape ciliary epithelial cells of upper respiratory tract and reach alveolar surface.
  • Progression to clinical disease depends on:
    • Number of M. tuberculosis organisms inhaled (infecting dose)
    • Virulence of these organisms
    • Host’s cell-mediated immune response
  • Bacilli ingested by pulmonary macrophages, where they are killed or continue to multiply.
    • Macrophages form granulomas to contain organisms.
  • M. tuberculosis can spread through bloodstream to infect any tissue or organ; most commonly infects posterior apical region of lungs.
  • Cell-mediated immunity occurs as well as delayed-type hypersensitivity.
    • After 1–3 months, tuberculin skin test will be positive.
    • ~90% of patients who experience primary disease have no further clinical manifestations other than positive skin test alone or in combination with radiographic evidence of stable granulomas.
  • Primary progressive disease seen in ~ 5% of patients
    • Children
    • Elderly
    • Immunocompromised
  • Reactivation disease develops in ~10% of patients, with nearly half of these cases occurring within 2 years of infection.
    • Most cases of TB in United States believed to result from reactivation.
  • Occasionally, massive inoculum of organisms may be introduced into bloodstream, causing widely disseminated disease and granuloma formation known as miliary TB.

  • Globally, 2 billion people infected and 2–3 million people die from TB each year.

  • Isolate patients to prevent spread of active disease.
  • Members of high-risk groups should be tested for TB infection and educated about disease (Table 1; Column 1 at highest risk for TB, followed by those in Column 2).

Table 1. Criteria for Tuberculin Skin Test Positivity by Risk Group

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