Preventing occupational disease and injury, second edition. Levy BS, Wagner GR, Rest KM, Weeks JL, eds. Washington, DC: American Public Health Association, 2005 Jan; :492-499
Tuberculosis (TB) is a bacterial disease caused by Mycobacterium tuberculosis. It is usually transmitted from person to person through the air when a person with TB in the lungs or throat coughs, sneezes, speaks, or sings. TB most often affects the lungs, but it can affect other parts of the body, such as the brain, kidneys, or spine. The initial infection rarely produces noticeable symptoms, but the infected person usually develops a delayed hypersensitivity immune response within 2 to 12 weeks after exposure, and may develop x-ray evidence of infection in the lung. Some people infected with TB progress from the initial infection to develop TB disease. General symptoms of TB disease include fatigue, fever, night sweats, and weight loss; lung symptoms include cough, chest pain, and hemoptysis (coughing up blood). Treatment with standardized regimens can cure TB disease and can prevent infected individuals from developing TB disease. The Mantoux tuberculin skin test (TST) is used to determine whether a person is infected with M. tuberculosis. This test is performed by injecting 0.1 milliliter of purified protein derivative tuberculin into the skin (intradermally) on the inner surface of the forearm. The site is evaluated for induration (swelling) 48 to 72 hours after administration. The size of the induration that is considered to represent a "positive" reaction varies according to the individual's risk factors, such as occupation, recent exposure history, and competency of the immune system. False-positive reactions may occur due to infection with mycobacteria other than M. tuberculosis or immunization with bacille Calmette-Guerin (BeG) vaccine. BeG is a strain of M. bovis, the organism that causes TB in cattle, which has been modified to produce immunity against TB without causing disease. BeG is the most widely used vaccine in the world, but it is generally not recommended in the United States because of the low risk of infection with M. tuberculosis, the variable effectiveness of the vaccine against pulmonary TB in adults, and interference by the vaccine with tuberculin reactivity.