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Course Sample:
Identification Tuberculosis (TB) is a mycobacterial disease important as a cause of disability and death in many parts of the world and is re-surfacing as a problem in the United States. The initial infection usually goes unnoticed. Tuberculin sensitivity appears within a few weeks of exposure and its lesions commonly heal, leaving no residual changes, except occasional pulmonary or tracheobronchial lymph node calcifications. Approximately 95% of those initially infected enter this latent phase from which there is lifelong risk of reactivation. In approximately 5% of patients, the intial infection may progress directly to pulmonary tuberculosis or, by lymphohematogenous dissemination of bacilli, to pulmonary, miliary, meningeal, or other extrapulmonary involvement. Serious outcome of the initial infection is more frequent in infants, adolescents, and young adults. Extrapulmonary tuberculosis is much less common than pulmonary. It may affect any organ or tissue and includes Tuberculosis meningitis, acute hematogeneous (miliary) tuberculosis and involvement of lymph nodes, pleura, pericardium, kidneys, bones, and joints, larynx, skin, intestines, peritoneum and eyes. Progressive pulmonary tuberculosis arises from exogenous reinfection or endogenous reactivation of a latent focus remaining from the initial infection. If untreated, about 50% of the patients will die within a two-year period. Appropriate chemotherapy results in a cure in most cases. Clinical status is based mainly upon the presence or absence of tubercle bacilli in the sputum as well as the nature of changes seen on chest x-rays. Abnormal x-ray densities are indicative of pulmonary infiltration. Cavitation and fibrosis can occur before clinical manifestations. Fatigue, fever, and weight loss may occur early, while localizing symptoms such as cough, chest pain, hemoptysis, and hoarseness become prominent in advanced stages. People who are or have been infected with Mycobacterium tuberculosis, M. African and M. bovis, will almost always react to a low dose tuberculin skin test, i.e., bio-equivalent to 5 International Units (IU) of the International Standard of Purified Protein Derivative-Standard (PPD-S). The reaction may be suppressed in critically ill tuberculosis patients, during certain acute infectious diseases, notably measles, by vaccination with live attenuated viruses, and in persons who either have an immunosuppression disease or on immunosupperssion drugs. Reactions caused by other mycobacteria, including BCG, tend to be smaller. Their relative frequency varies with the prevalence of these other mycobacteria in the environment. When non-specific sensitivity is prevalent, a positive reaction is usually defined as one with a diameter of > 10mm of in duration. This must be recognized as an arbitrary cut-point and not suitable for all situations and age groups. The cut-point for true positive reactions will vary and may be as high as an induration of 15mm in diameter for adults living in areas with little tuberculosis, but a high frequency of other mycobacterium. On the other hand, among household contacts of infectious tuberculosis cases and persons with HIV infection, as little as 5mm of tuberculin testing of adults is done. A subsequent reaction, with an increase in size to a diameter which meets the criteria for a positive reaction in the population being tested is considered conversion indicative of a recent tuberculosis infection. This definition is also arbitrary. The larger the increase in reaction size and the absolute size of reaction, the greater the likelihood of recent tuberculosis infection. Tuberculosis infection may also be inferred when a single test presents > 10mm of induration. |
