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FOUNDATION OVERVIEW

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Tuberculosis (TB) is an infection caused by the acid-fast bacillus (AFB) Mycobacterium tuberculosis. Transmission of TB is person to person through inhalation of droplet nuclei in the air. The majority of patients infected with M. tuberculosis have latent tuberculosis infection and do not develop active, symptomatic, disease. Approximately 10% of patients develop active disease if not treated with isoniazid. Risk of active disease is highest in the first 2 years after infection.

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Tuberculosis primarily affects the lungs. The clinical presentation of pulmonary TB includes: productive cough, fever, weight loss, night sweats, and hemoptysis. Extrapulmonary TB develops in genitourinary, skeletal, central nervous system, and the pericardial system. Disseminated TB occurs in several parts of the body.

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Targeted tuberculin skin testing is used to identify patients with TB. The Mantoux test injects a tuberculin purified protein derivative (PPD) intradermally on the inner portion of the forearm. The induration at the injection site is evaluated in 48 to 72 hours. The size of the induration and the patient’s risk determine whether the test is read as positive (Table 29-1). Patients who have previously received the Bacillus Calmette-Guerin vaccine in another country can have a positive skin test due to the vaccine. This vaccination is not recommended for most of the US population. The QuantiFERON-TB Gold In-Tube test measures the level of interferon γ released in a blood sample in response to PPD. This test provides a rapid diagnosis confirmation compared to skin testing. The Centers for Disease Control has said it can be used in place of skin testing in individuals older than 5 years of age. Sputum cultures, chest radiographs, and drug susceptibilities are obtained at first suspicion of active disease.

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TABLE 29-1Criteria for Tuberculin Positivity by Risk Group

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