Global and Regional Burden and Trands

Global and Regional Burden and Trands - Based on surveys of the prevalence of infection and of disease, on assessments of the performance of surveillance systems and on death registrations, there were an estimated 9.2 million new cases of TB in 2006, of which 4.1 million were smear-positive. The WHO African region had the highest estimated incidence rate (363 per 100,000 population), but the majority of TB patients live in the most populous countries of Asia. Five countries – Bangladesh, China, India, Indonesia, and Pakistan – have almost half the world’s population (46%) and produced about half (48%) of all new TB cases arising worldwide in 2006. Illustrates the global distribution of new TB cases in 2006, in terms of numbers and rates per 100,000 population.

Estimated of new cases of Tuberculosis 1997

map the spread of Tuberculosis

Much of the work of the WHO and partners focuses on the 22 countries known as the high-burden countries (HBCs). These are the countries which, in 2002, were estimated to have had the highest numbers of incident TB cases in the year 2000: Afghanistan, Bangladesh, Brazil, Cambodia, China, the Democratic Republic of the Congo, Ethiopia, India, Indonesia, Kenya, Mozambique, Myanmar, Nigeria, Pakistan, Philippines, the Russian Federation, South Africa, Thailand, Uganda, the United Republic of Tanzania, Viet Nam and Zimbabwe. Changes in estimates due to new data or techniques, and likely changes in incidence rates and population sizes, mean that this list no longer exactly matches the list of the 22 countries with the largest number of new cases each year, but it is still true that, between them, the HBCs account for 80% of new TB cases arising annually. shows the estimated incidence and prevalence of TB and mortality from TB for 2006. Globally an estimated 1.7 million people died from TB in 2006, 231,000 of them infected with HIV.

Estimates of TB incidence, prevalence and mortality are uncertain, and rely to varying degrees on assumptions about the quality of surveillance data, about the quality and impact of treatment and about the duration of disease and case-fatality rates. New methods for evaluating the burden of TB and impact of control are needed. In our view these should be based principally on assessments of the quality of surveillance systems, backed by data obtained from surveys of the prevalence of disease. These methods and the resulting data would help to meet increasing demands from donor agencies (such as the Global Fund to Fight AIDS, Tuberculosis, and Malaria) to demonstrate the impact of the activities which they fund, and of international experts to increase the transparency surrounding statistics provided through databases such as those of the WHO  A recently established task force on measurement of TB will guide work on improving estimates of the burden of TB and the impact of control.

Estimates of the incidence of multidrug-resistant TB (MDR-TB; caused by strains of M. tuberculosis resistant to at least isoniazid and rifampicin) are even more uncertain than those of overall TB incidence. Drug susceptibility testing is not widely available, although WHO guidelines for incorporating the diagnosis and treatment of drug-resistant TB into the routine activities of national TB control programmes are likely to lead to improved information about the proportion of TB cases which are MDR. Current estimates (based on multivariate analysis) are that 489,000 cases of MDR-TB arose in 2006 among new and previously treated TB cases.

Extensively drug-resistant TB (XDR-TB) is defined as TB due to bacilli resistant to any fluoroquinolone, and at least one of three injectable second-line drugs (capreomycin, kanamycin, and amikacin), in addition to isoniazid and rifampicin. The magnitude of the XDR-TB problem globally is not yet known. Where the transmission of M. tuberculosis has been stable oincreasing for many years, the incidence rate is relatively high among infants and young adults, and most cases are due to recent infection or reinfection. As transmission falls, the caseload shifts to older adults, and a higher proportion of cases comes from the reactivation of latent infection. Therefore, in the countries of Western Europe and North America that now have low incidence rates, indigenous TB patients tend to be elderly, while patients who are immigrants from highincidence countries tend to be young adults.

Allowing for the difficultiesof diagnosing childhood TB, estimation exercises indicate that there are relatively few cases among 0–14 year olds; while this age group accounts for nearly 30% of the world’s population, it accounts for only 12% of estimated cases. In 2006, countries reported 1.6 million smear-positive TB cases among men, but only 884,000 among women. In some instanceswomen have poorer access to diagnostic facilities, but the broader pattern also reflects real epidemiological differences between the sexes: while there is some evidence that young adult women (15–44 years) are more likely than men to develop active TB following infection, this effect is typically outweighed by the much higher exposure and infection rates among adult men