Prevalence of Latent Tuberculosis in High Risk Children Attending Pediatric Hospital of Assiut University

TB is an infectious disease caused by the bacillus Mycobacterium tuberculosis. It typically affects the lungs (pulmonary TB) but can also affect other sites (extrapulmonary TB). The disease is spread when people who are sick with pulmonary TB expel bacteria into the air, for example by coughing. Overall, a relatively small proportion (5-15%) of the estimated 1.7 billion people infected with M. tuberculosis will develop TB disease (active disease) during their lifetime. However, the probability of developing TB disease is much higher among people infected with HIV, and also higher among people affected by risk factors such as under-nutrition, diabetes, smoking and alcohol consumption. Latent tuberculosis infection (LTBI) is defined as a state of persistent immune response to stimulation by Mycobacterium tuberculosis antigens with no evidence of clinically manifest active TB. As there is no "gold standard" test for LTBI, the global burden is not known with certainty; however, up to one third of the world's population is estimated to be infected with M. tuberculosis , and the vast majority have no signs or symptoms of TB disease and are not infectious, although they are at risk for active TB disease and for becoming infectious. Several studies have shown that, on average, 5-10% of those infected will develop active TB disease over the course of their lives, usually within the first 5 years after initial infection . The risk for active TB disease after infection depends on several factors, the most important being immunological status