Chapter 10-11: Tuberculosis (TB)

TEXTBOOK PRESENTATION

TB pneumonia usually develops due to reactivation of latent mycobacteria residing in the upper lobes. Symptoms are chronic and include cough, fever, weight loss, and night sweats. By the time patients seek medical attention, they have often had these symptoms for weeks or months. The weight loss and duration of symptoms often suggest cancer.

DISEASE HIGHLIGHTS

1. Obligate aerobe that has predilection for lung apices.

2. The organism is slow growing; the generation time is 20–24 hours, resulting in slow progression.

3. Common and serious

   1. Infects 33% of the world’s population

   2. 8.6 million new cases per year (2014 data) and 1.5 million deaths (worldwide)

   3. 95% of cases occur in developing countries.

4. Epidemiology

   1. An estimated 11 million persons are infected with TB in the United States.

   2. Foreign-born persons have the highest rate of TB (13.4 times higher than US-born persons) and account for 66% of TB cases in the United States and 85% of multidrug-resistant TB (MDR-TB resistant to isoniazid and rifampin).

   3. Asians, blacks, and Hispanics have higher rates of TB than whites (22.9, 8.3, and 7.4 times, respectively). Foreign-born persons account for a majority of TB cases in Asians and Hispanics but not blacks.

   4. 67% of cases occur in the nonwhite population.

   5. In the nonwhite population, the median age is 39. In whites, the median age is 62.

   6. Reactivation TB accounts for 90% of TB in older patients and 67% of TB in younger patients.

   7. High-risk groups

      1. HIV

         1. HIV-infected patients are at highest risk for TB (200 times increased incidence).

         2. In 2011, HIV-infected persons accounted for 1.1 million TB cases worldwide (13% of the total).

         3. TB may be the first manifestation of HIV.

            Patients with active or latent TB should be tested for HIV.

         4. Extrapulmonary TB without pulmonary disease is more common in patients with AIDS (30%) than in those without AIDS (15%).

         5. The presentation of pulmonary TB in early HIV infection is similar to that in immunocompetent persons; whereas, in advanced HIV infection, TB presents in more atypical ways.

      2. Alcoholics

      3. Other high-risk groups

         1. Foreign-born persons

         2. Immunosuppressed patients (including patients taking corticosteroids)

         3. Patients with cancer, diabetes mellitus, end-stage renal disease, transplants, or malnutrition

         4. PPD-positive patients

         5. Patients with evidence of prior TB on chest film

         6. Economically disadvantaged, inner city residents

         7. Nursing home residents

         8. Drug-dependent persons, homeless persons, prison inmates

5. Pathophysiology

   1. Inhaled organism lands in the middle and lower lobes (due to increased ventilation).

   2. Multiplies over next 3 weeks, spreads to hilar nodes and often bloodstream, seeding more distant anatomic sites.

   3. Organism reproduces preferentially in areas of high PaO₂ (lung apices, renal cortex, vertebrae).

   4. In 90% of patients, the immune system then contains the organism resulting in typical scarring (Ghon complex). However, the chest film can be normal.

   5. Above sequence usually asymptomatic.

   6. In some patients, a few viable organisms remain. This is referred to as latent TB infection. Latent TB can reactivate later (reactivation TB).

   7. The PPD is positive 6–8 weeks after the initial infection. These ...