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INTRODUCTION

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  • Tuberculosis (TB) is a communicable infectious disease caused by Mycobacterium tuberculosis. It can produce silent, latent infection, as well as progressive, active disease. Globally, 2 billion people are infected and roughly 1.5 million people die from TB each year.

  • M. tuberculosis is transmitted from person to person by coughing or other activities that cause the organism to be aerosolized. Close contacts of TB patients are most likely to become infected.

  • Human immunodeficiency virus (HIV) is the most important risk factor for progressing to active TB, especially among people 25 to 44 years of age. An HIV-infected individual with TB infection is over 100-fold more likely to develop active disease than an HIV-seronegative patient.

  • Approximately 90% of patients who experience primary disease have no further clinical manifestations other than a positive skin test either alone or in combination with radiographic evidence of stable granulomas. Tissue necrosis and calcification of the originally infected site and regional lymph nodes may occur, resulting in the formation of a radiodense area referred to as a Ghon complex.

  • All clinical specimens suspected of containing mycobacteria should be cultured.

  • Approximately 5% of patients (usually children, the elderly, or the immunocompromised) experience progressive primary disease at the site of the primary infection (usually the lower lobes) and frequently by dissemination, leading to meningitis and often to involvement of the upper lobes of the lung as well.

  • Approximately 10% of patients develop reactivation disease, which arises subsequent to the hematogenous spread of the organism. In the United States, most cases of TB are believed to result from reactivation.

  • Occasionally, a massive inoculum of organisms may be introduced into the bloodstream, causing widely disseminated disease and granuloma formation known as miliary TB.

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CLINICAL PRESENTATION AND DIAGNOSIS

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  • The classic presentation of pulmonary TB is weight loss, fatigue, a productive cough, fever, and night sweats (Table 49–1). The onset of TB may be gradual. Physical examination is nonspecific but suggestive of progressive pulmonary disease.

  • Clinical features associated with extrapulmonary TB vary depending on the organ system(s) involved but typically consist of slowly progressive decline of organ function with low-grade fever and other constitutional symptoms.

  • Patients with HIV may have atypical presentation. HIV-positive patients are less likely to have positive skin tests, cavitary lesions, or fever. They have a higher incidence of extrapulmonary TB and are more likely to present with progressive primary disease.

  • TB in the elderly is easily confused with other respiratory diseases. It is far less likely to present with positive skin tests, fevers, night sweats, sputum production, or hemoptysis. TB in children may present as typical bacterial pneumonia and is called progressive primary TB.

  • The most widely used screening method for tuberculous infection is the tuberculin skin test, which uses purified protein derivative (PPD). Populations most likely to benefit from skin testing are listed in Table 49–2.

  • The Mantoux method of PPD administration consists of the intracutaneous ...

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