A. Worldwide, 1.7 to 2 million persons die each year from tuberculosis (TB).

B. The changing epidemiologic features and resistance patterns of TB make this disease more difficult to recognize and treat for all health care providers, including those in the intensive care setting.

C. Prompt recognition of TB and early institution of effective therapy will allow successful treatment of the patient and the prevention of transmission.

D. Most patients with localized disease who adhere to a full course of anti-TB therapy are cured.

A. TB is usually a subacute or chronic illness caused by Mycobacterium tuberculosis (MTB), also known as an acid-fast staining bacillus (AFB).

1. MTB commonly infects the lung but may also cause disease in other organs of the body.

A. Primary infection.

1. Usually asymptomatic: Tubercle bacilli gain entry into the lungs, and then are phagocytized by alveolar macrophages. In most patients, a localized inflammatory process occurs with the development of granulomas.

2. In some individuals, the bacilli multiply in the lungs and cause extensive regional lymphadenitis, which produces symptoms.

3. Primary infection may disseminate in the bloodstream and seed the central nervous system (CNS), liver, spleen, kidney, and other organ systems (rare in adults).

4. Tuberculin skin test (TST) usually becomes positive 2 to 10 weeks after the primary infection.

B. Latent TB.

1. Classically characterized by a positive TST and lack of symptoms or signs of active disease.

2. Interferon-γ release assays (IGRAs) using whole blood detect latent infection and may be used as an alternative to the TST particularly in
foreign-born persons who have had Bacillus Calmette-Guèrin (BCG) vaccine. The tests use antigens not present in BCG, so cross-reactivity is not observed.

3. Immunocompetent persons develop a granulomatous inflammatory process and usually control but do not eradicate MTB infection.

4. Chest x-ray (CXR) is normal.

C. Active TB.

1. Occurs in approximately 10% of immunocompetent individuals infected with MTB over their lifetime.

a. Half of these cases develop within the first 1 to 2 years after infection.

b. The other half may occur at any point during an individual’s lifetime (reactivation disease).

2. Associated with classic symptoms of cough, hemoptysis, fevers, night sweats, and weight loss.

3. In patients with defects in cell-mediated immunity, the risk of progressive primary, reactivation, or disseminated disease is increased.

a. The annual risk of developing active TB is 5% to 7% among human immunodeficiency virus (HIV)-infected persons with latent TB infection.

b. These patients often have poorly formed granulomas, have higher AFB burden in tissues, and may have atypical presentations.

A. Patients critically ill from TB often have predisposing risks and/or comorbidities.

1. High-risk patients.

a. History of latent TB (by positive TST and/or IGRA) or prior active TB.

b. Contact with known or suspected active TB case.

c. Immigration from countries with a high incidence of TB.

d. Presence of fibrotic lung lesions or upper lobe scarring.

e. Advanced age.

f. Alcohol or other drug use.

g. Institutional exposure (i.e., correctional facilities, homeless shelters).

h. Immunocompromised host (HIV infection, chemotherapy, immunosuppressive therapy following organ transplantation, or use of steroids or anti-tumor necrosis factor agents).

2. There can also be critical involvement of multiple organ systems.

a. Lungs: respiratory failure from fulminant tuberculous pneumonia, life-threatening (severe) hemoptysis, or acute respiratory distress syndrome (ARDS).

b. Cardiac: pericardial tamponade from pericardial TB.

c. CNS: TB meningitis.

d. Gastrointestinal (GI): TB enteritis and perforation, pancreatitis.

e. Systemic: disseminated TB with hepatosplenomegaly and pancytopenia.

B. Chest radiograph or chest computed tomography (CT) is the primary diagnostic and screening test for active TB.

1. Immunocompetent patients with pulmonary TB usually have abnormal CXR or chest CT findings.

a. Primary or childhood TB: lower lobe infiltrate (Ghon focus) with ipsilateral hilar adenopathy (Ghon complex, especially in children).

b. Reactivation or adult pulmonary TB: fibrotic and/or cavitary infiltrates in the apical segment of the upper lobes, superior segment of the lower lobes.

c. Primary TB infections in adults may present with either classic “primary” or “reactivation” radiologic findings.

d. Disseminated (miliary) disease: diffuse nodules 1 to 3 mm in size.

e.

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