Background
Public health aspects
Human TB has existed for thousands of years. No country is TB-free, and the disease is endemic in most poor countries of the world. It is estimated that about one-third of the current global population is infected asymptomatically with Mtb, of whom 5-10% will develop clinical disease during their lifetime. According to WHO estimates for 2001, there are 16-20 million cases of TB worldwide, with more than 8 million new cases and over 1.8 million deaths each year. Most new cases and deaths occur in developing countries where infection is often acquired in childhood. The annual risk of TB infection in children in high-burden countries is estimated to be 0.5-2%. Childhood deaths from TB are usually caused by meningitis or disseminated disease.
Co-infection with Mtb and HIV has been shown to be a lethal combination. In areas of sub-Saharan Africa where HIV is most prevalent, the annual incidence of TB has risen to more than 300 cases per 100 000 inhabitants. In some of these places, nearly 50% of the HIV-infected population is co-infected with TB and more than two-thirds of TB patients are infected with HIV. For HIV-infected persons, the liftime risk of developing TB disease is as high as 30-50%. In some parts of south-east Asia, an estimated 20-25% of TB cases will be directly attributable to HIV within the next few years. In most industrialized countries, decades of declining TB incidence halted towards the end of the 20th century when increasing annual numbers of TB cases were recorded. In several regions of the former Soviet Union, the recent rise in TB incidence has been dramatic. In industrialized settings, new cases of TB usually occur in the elderly. In recent years, however, TB has also been found increasingly in immigrants from endemic countries, in HIV-positive individuals and in socially deprived groups including drug-dependent individuals and prisoners.