<P> Progression from TB infection to overt TB disease occurs when the bacilli overcome the immune system defenses and begin to multiply . In primary TB disease (some 1--5% of cases), this occurs soon after the initial infection . However, in the majority of cases, a latent infection occurs with no obvious symptoms . These dormant bacilli produce active tuberculosis in 5--10% of these latent cases, often many years after infection . </P> <P> The risk of reactivation increases with immunosuppression, such as that caused by infection with HIV . In people coinfected with M. tuberculosis and HIV, the risk of reactivation increases to 10% per year . Studies using DNA fingerprinting of M. tuberculosis strains have shown reinfection contributes more substantially to recurrent TB than previously thought, with estimates that it might account for more than 50% of reactivated cases in areas where TB is common . The chance of death from a case of tuberculosis is about 4% as of 2008, down from 8% in 1995 . </P> <P> Roughly one - third of the world's population has been infected with M. tuberculosis, with new infections occurring in about 1% of the population each year . However, most infections with M. tuberculosis do not cause TB disease, and 90--95% of infections remain asymptomatic . In 2012, an estimated 8.6 million chronic cases were active . In 2010, 8.8 million new cases of TB were diagnosed, and 1.20--1.45 million deaths occurred, most of these occurring in developing countries . Of these 1.45 million deaths, about 0.35 million occur in those also infected with HIV . </P> <P> Tuberculosis is the second-most common cause of death from infectious disease (after those due to HIV / AIDS). The total number of tuberculosis cases has been decreasing since 2005, while new cases have decreased since 2002 . China has achieved particularly dramatic progress, with about an 80% reduction in its TB mortality rate between 1990 and 2010 . The number of new cases has declined by 17% between 2004 and 2014 . Tuberculosis is more common in developing countries; about 80% of the population in many Asian and African countries test positive in tuberculin tests, while only 5--10% of the US population test positive . Hopes of totally controlling the disease have been dramatically dampened because of a number of factors, including the difficulty of developing an effective vaccine, the expensive and time - consuming diagnostic process, the necessity of many months of treatment, the increase in HIV - associated tuberculosis, and the emergence of drug - resistant cases in the 1980s . </P>

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