Tuberculosis (TB)

WHO report 2008
Global tuberculosis control

1.9 Summary

There were an estimated 9.2 million new cases of TB in 2006, of which 709 000 (8%) were HIV-positive. This is an increase from 2005, reflecting population growth in Asia, Africa and Europe. The countries that rank first to fifth in terms of absolute numbers of cases are India, China, Indonesia, South Africa and Nigeria, while Africa has the highest incidence rate per capita (linked to HIV) and accounts for 12 of the 15 countries with the highest TB incidence rates. There were an estimated 1.7 million deaths due to TB in 2006, of which 0.2 million were among HIV-positive people, and 14.4 million prevalent cases. These statistics show that TB remains a major global health problem.

More positively, the TB incidence rate per capita is declining globally, and in five out of the six WHO regions (it is approximately stable in Europe). The latest data indicate that the TB incidence rate has been falling globally since 2003. If this is confirmed by further monitoring, MDG 6 Target 6.C, to halt and reverse the incidence of TB, will be achieved well before the target date of 2015. Prevalence and deaths rates are also falling, and at a faster rate than TB incidence. Based on trends for the last five years, the Stop TB Partnership targets of halving prevalence and death rates by 2015 compared to 1990 could be achieved in the South-East Asia, Western Pacific and Eastern Mediterranean regions, and in the Region of the Americas. However, they are unlikely to be achieved globally based on current trends, due to two regions - the European and African regions - being far from the targets.

In addition to the impact indicators of incidence, prevalence and mortality, progress in TB control can also be assessed with reference to the outcome targets first set by the World Health Assembly in 1991: to detect at least 70% of new (incident) cases of smear-positive TB in DOTS programmes, and to successfully treat 85% of those cases that are detected. In 2005, the treatment success rate globally was 84.7%, just a fraction of one percent below the target, representing a further improvement from previous years despite a 10-fold increase in the annual number of patients treated in DOTS cohorts since 1994. This high average rate conceals the fact that treatment success rates remain well below the target in the European Region and in the Region of the Americas, and indeed the latest data show a worrying deterioration rather than progress in these two regions. With 5.3 million cases notified in DOTS programmes (98% of the total notified globally), of which 2.5 million were new smear-positive cases (99% of the total notified globally), the case detection rate for new smear-positive TB under DOTS is estimated at 61% globally (62% when notifications from non-DOTS programmes are included). The target of 70% has been exceeded in the Western Pacific Region and is close to being achieved in South-East Asia and the Region of the Americas. Increasing DOTS coverage in the Region of the Americas, and increasing both DOTS coverage and the use of smear microscopy in the European Region, could enable both of these regions to achieve the target for case detection. A total of 58 countries met the target for treatment success in 2005, 77 are assessed to have met the target for case detection in 2006, and 32 countries as well as the Western Pacific Region as a whole appear to have met both targets in 2005–2006.

While continued improvement in treatment success and case detection rates is encouraging, there has been a deceleration in the rate of progress in case detection globally, and the rate of 61% achieved in 2006 is behind the Global Plan milestone of 65%. China and India account for 28% of the estimated number of undetected cases, but there was almost no improvement in case detection in either country during 2006. Most of the remaining cases estimated to be undetected are in Africa. This suggests that further progress in case detection globally will depend to a great extent on progress in the African Region, and on further progress in China and India. For the African Region, there is an important caveat, however. It is possible that rates of case detection are currently underestimated, due to the difficulty of disentangling the effect of improved case-finding and the HIV epidemic on TB notifications. Further analytical work of the kind already done in Kenya, and new surveys conducted as part of the impact measurement work discussed in Chapter 2, will help to improve our current estimates of case detection in Africa.

New analytical work is also improving our understanding of the extent to which TB control programmes are driving trends in TB incidence, working with or against other biological, social and economic factors. The ecological analysis presented in this chapter suggests that while DOTS programmes have reduced deaths and prevalence, they have not yet had a major impact on TB transmission and incidence around the world. These observations lay down a challenge: to show that the diagnosis of active TB can be made early enough, and that cure rates can be high enough, to have a substantial impact on incidence on a large geographic scale. The greater the impact on incidence, the more likely it is that prevalence and deaths will be halved by the MDG deadline of 2015.