TuberculosisIntroductionTuberculosis (TB) is an ancient disease, traces of which have been found in human remains dating back more than 9,000 years, to the Neolithic era. 1 It was identified and described by Hippocrates as early as 460 BC. and continued to be documented in places such as ancient Rome, Egypt, India and China. 2 3 4 5The disease can be caused by different mycobacteria such as Mycobacterium bovis, M. africanum, M. canettii, M. microti and, most commonly, M. tuberculosis; although all five are very similar and together are called the Mycobacterium tuberculosis complex (MTBC). Recently, two additional organizations. Mycobacterium pinnipedii and Mycobacterium caprae have also been implicated in human disease. 6, 7 MTBC members are long, rod-shaped, Gram-positive bacteria with unique characteristics such as an exceptionally slow growth rate and high lipid content in their cell wall that provide protection against degradation and may explain their persistent survival. in the environment even after the death of a host. 8Active tuberculosis only develops in around 10% of infected people, remaining latent in the rest; although latent infection can progress to active disease years later, particularly in immunocompromised individuals. 9 MTBC infection can affect any organ in the body, but clinical presentation is most common in the lungs (pulmonary TB). General symptoms include fever, loss of appetite, weight loss, fatigue and severe cough with bloody sputum (hemoptysis) which can lead to death if left untreated. 10 Mortality rates without treatment are high: in a study of the natural history of tuberculosis in HIV-negative patients, 70% died within 10 years. 11 Tuberculosis remains a major health problem worldwide... middle of paper ...... as better ventilation, negative pressure rooms and the use of UV light for disinfection, nosocomial transmissions continue to pose a problem, perhaps because they are iatrogenic and cases may go unnoticed due to underdiagnosis. 16Contagiousness Tuberculosis infection rates are high, particularly with frequent or close contact with people with active tuberculosis. One study estimates an infection rate of around 22% and a diagnosis with a positive sputum smear is the best indicator of contagiousness. 19 However, contrary to popular belief, sputum smear-negative patients are also contagious, with a study in San Francisco attributing 17% of transmissions to such cases. 20Researchers have also identified a list of other factors associated with TB transmission, such as environmental, organismal and host factors, but these are unfortunately beyond the scope of this article.. 16