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Key Features

Essentials of Diagnosis

  • Fatigue, weight loss, fever, night sweats, and productive cough

  • Risk factors for acquisition of infection: household exposure, incarceration, drug use, travel to an endemic area

  • Chest radiograph: pulmonary opacities, most often apical

  • Sputum smear positive for acid-fast bacilli or sputum culture positive for Mycobacterium tuberculosis

General Considerations

  • Primary infection

    • Occurs with inhalation of airborne droplets containing viable tubercle bacilli and subsequent lymphangitic and hematogenous spread before immunity develops

    • Up to one-third of new urban cases are from primary infection acquired by person-to-person transmission

  • Latent tuberculosis infection (LTBI)

    • Occurs when bacilli are contained within granulomata

    • Nontransmissible while latent, but may become active disease if the infected person's immune function becomes impaired

  • Drug-resistant strains of M tuberculosis are increasingly common worldwide, though rates in the US have fallen to less than 1.3%

  • Risk factors for drug resistance include

    • Immigration from countries with a high prevalence of drug-resistant tuberculosis

    • Close and prolonged contact with individuals with drug-resistant tuberculosis

    • Unsuccessful previous antituberculosis therapy

    • Patient nonadherence to such therapy

  • Resistance may be to single or multiple drugs

    • Drug-resistant tuberculosis is resistant to one first-line antituberculous drug, either isoniazid (INH) or rifampin (RIF)

    • Multidrug-resistant tuberculosis (MDR-TB) is resistant to INH and RIF, and possibly additional agents

    • Extensively drug-resistant tuberculosis (XDR-TB) is resistant to INH, RIF, fluoroquinolones and either aminoglycosides or capreomycin or both

  • Nonadherence is a major cause of treatment failure, disease transmission, and development of drug resistance

Demographics

  • Infects one-third of the world's population

  • In 2014, there were 9.6 million new cases of tuberculosis worldwide with 1.5 million people dying of the disease

  • In the United States, an estimated that 11 million people are infected with M tuberculosis and in 2014 there were 9421 active cases

  • Occurs disproportionately among malnourished, homeless, and marginally housed individuals

  • Risk factors for reactivation

    • Gastrectomy

    • Silicosis

    • Diabetes mellitus

    • HIV

    • Immunosuppressive drugs

  • Risk factors for drug resistance

    • Immigration from regions with drug-resistant tuberculosis

    • Close contact with patients infected with drug-resistant tuberculosis

    • Unsuccessful prior antituberculosis therapy

    • Patient noncompliance with such treatment

Clinical Findings

Symptoms and Signs

  • Cough is the most common symptom

  • Blood-streaked sputum is common, frank hemoptysis is rare

  • Slowly progressive constitutional symptoms include malaise, anorexia, weight loss, fever, and night sweats

  • Patients appear chronically ill

  • Chest examination is nonspecific; post-tussive apical rales are classic

  • Atypical presentations are becoming more common, usually among the elderly and HIV-positive patients

Differential Diagnosis

  • Pneumonia

  • Lung abscess

  • Lung cancer or lymphoma

  • Mycobacterium avium complex (or other nontuberculous mycobacterial infection)

  • Sarcoidosis

  • Fungal infection, eg, histoplasmosis

  • Endocarditis

  • Silicosis or asbestosis

  • Nocardiosis

Diagnosis

Laboratory Tests

  • Tuberculin skin test (TST) for LTBI

    • The Mantoux test is the preferred method: 0.1 mL of purified protein derivative (PPD) containing 5 tuberculin units ...

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