Epidemiology of tuberculosis

Tuberculosis is an ancient disease that remains a major global health problem. It is primarily transmitted by the respiratory route. Prolonged exposure to an infectious person is generally required for the infection to be transmitted. It is estimated that one third of the world's population is infected with Mycobacterium tuberculosis. The risk of developing tuberculosis following infection with M. tuberculosis has been estimated at 5-10% in a lifetime with the highest risk in the first 2 yrs after infection. Human immunodeficiency virus (HIV) infection is the most potent risk factor for development of tuberculosis after infection, with an annual risk of progression to disease of 3-13%. It is estimated that 7.5 million cases of tuberculosis occurred world-wide in 1990, increasing to 8.8 million in 1995, of which 95% were in low-income countries. This number is projected to rise to 10.2 million by the year 2000. Without treatment, 50-60% of tuberculosis cases would die within a five year period. Despite the availability of an effective treatment, an estimated 3 million persons died of tuberculosis in 1995, of which 98% were in low-income countries. After decades of decline, the incidence of tuberculosis in Europe rose during the last 10 yrs. The cause of this increase varies by country, with immigration from high prevalence countries, poverty and HIV being important factors. In the former USSR, increasing notification rates are due to a combination of economic recession, malnutrition and poor living conditions. In low-income countries, the incidence of tuberculosis has risen dramatically particularly in Sub- Saharan Africa. The major causative factor is the HIV epidemic. The already high HIV-seroprevalence among tuberculosis cases is predicted to increase further in SubSaharan African countries. In southeast asian countries, the HIV seroprevalence is also on the increase. Unless effective tuberculosis programmes are implemented in all countries, the global burden of tuberculosis will continue to increase.