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SOURCE

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Source: Namdar R, Lauzardo M, Peloquin CA. Tuberculosis. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw-Hill; 2017. http://accesspharmacy.mhmedical.com/content.aspx?bookid=1861&sectionid=146071982. Accessed May 9, 2017.

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CONDITION/DISORDER SYNONYMS

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  • Tuberculosis (TB)

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DEFINITION

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  • Communicable infectious disease.

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

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ETIOLOGY

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  • Caused by Mycobacterium tuberculosis, a bacillus.

  • Transmitted by coughing or other activities that cause the organism to be aerosolized.

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PATHOPHYSIOLOGY

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  • 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.

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EPIDEMIOLOGY

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  • Globally, 2 billion people infected and 1.5 million people die from TB each year.

  • In the United States, an estimated 9 million people are latently infected with M. tuberculosis.

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RISK FACTORS FOR INFECTION

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  • HIV, especially from 25 to 44 years of age.

    • More likely to have active TB

  • Location and place of birth.

    • Distribution uneven across the United States.

      • California, Florida, New York, and Texas accounted for 51% of the TB cases reported nationally in 2014.

      • Close contacts of pulmonary TB patients such as family members, coworkers, or coresidents in places such as prisons, shelters, or nursing homes are the most likely to become infected.

    • More common in foreign-born persons.

  • Race, ethnicity, age.

    • In the United States, disproportionately affects:

      • Hispanics, Blacks, and Asians.

      • People aged 25–44 years.

      • More common in older whites and Asians due to reactivation of latent infection.

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RISK FACTORS FOR DISEASE

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  • Once infected with M. tuberculosis, lifetime risk of active TB is ~10%.

  • Greatest risk occurs during first 2 years after infection.

  • Greater risk ...

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