Monitoring progress in TB control
This report draws four main conclusions about progress in TB control, based on routine monitoring and surveillance data. The first is that NTPs worldwide narrowly missed the 2005 targets for case detection (60%/70%) and treatment success (84%/85%). However, both targets were met in the Western Pacific Region, and in 26 countries including China, the Philippines and Viet Nam. Second, while the total number of patients diagnosed and treated under DOTS approached target levels in 2005, the numbers known to be HIV-positive or carrying drug-resistant bacteria (MDR-TB) were far fewer than anticipated by the Global Plan to Stop TB in 2006. Therefore a major effort is needed to step up collaborative TB/HIV activities and the management of MDR-TB. Third, the global TB epidemic appears to be on the threshold of decline. The incidence rate (per capita) worldwide has evidently stabilized or begun to fall, following the earlier downturns in prevalence and mortality.1 The incidence rate is now stable or falling in all WHO regions, including Africa and Europe. This result, if robust, means that MDG target 8 was met before 2005, and more than 10 years before the target date of 2015. However, the total number of new TB cases was still rising slowly in 2005, and in the African, Eastern Mediterranean and South-East Asia regions. In some Asian countries that report high rates of case detection and treatment success, incidence has not apparently been reduced as quickly as expected, for reasons that are not fully understood. This is linked to the fourth conclusion: that the global TB burden is not yet falling fast enough to satisfy the more demanding targets set by the Stop TB Partnership within the MDG framework. That is, at the current rate of progress, the 1990 prevalence and mortality rates will not be halved worldwide by 2015. The following sections discuss these conclusions in more detail.
The point estimate of the global case detection rate is 2005 is 60%, i.e. 10% below target. The data suggest that the target was reached in the Western Pacific Region and in seven HBCs. Calculations that attempt to allow for many of the uncertainties surrounding the point estimate indicate that case detection could have been as high as 69% or as low as 52%. It therefore seems unlikely that case detection exceeded 70%, both on the basis of these calculations and in view of much independent data showing why detection and/or reporting of patients is low in some places. For example, improving links among public health providers, and between public and private sectors, can substantially increase the number of patients reported to NTPs.2 3
While the case detection rate accelerated markedly between 2000 and 2004, the annual increase slowed between 2004 and 2005. Saturation in case-finding is expected where detection rates are high, but the deceleration began in South-East Asia, the Americas and the Western Pacific Region at rates of detection that were below the 70% target. Among HBCs, the slowdown was conspicuous in India, where the final stages of national DOTS expansion are taking place in states with the weakest health systems, such as Bihar and Jharkhand.
Case detection inevitably becomes more difficult at the limits of public health systems, but there are still some comparatively easy gains to be made. Several WHO reports in this series have emphasized that, in the Americas and Europe, many TB cases are reported through the public health system but from outside DOTS programmes. This implies that target rates of case detection could be achieved in these two regions by implementing the procedures required under DOTS, including the more frequent use of smear microscopy in the European Region. In other parts of the world, especially the African and the Eastern Mediterranean regions, case detection must be improved by finding more patients in total, for example by increasing the number and diversity of clinics and hospitals that report TB cases.
The acceleration in case detection since 2000 has been achieved both by improving detection within established DOTS areas and by expanding geographical coverage. However, “coverage” is now less useful as an indicator than in the early years of DOTS expansion, for two reasons. First, geographical coverage was high in most DOTS countries by 2005. Second, other determinants of case detection (e.g. diagnosis and treatment in the private sector, the efficiency of public health services) have, in many countries, become more important than recruiting new districts and provinces to DOTS programmes.
Outcomes of treatment
DOTS programmes treated more than two million smear-positive patients in the 2004 cohort, and achieved a global success rate just below the 85% target. The target was met in the South-East Asia and Western Pacific regions, and in eight HBCs. However, the overall treatment success, coupled with the 54% case detection rate in 2004, means that less than half (46%) of all new smear-positive patients were known to have been successfully treated in that cohort.
In the countries where treatment outcomes have been poor in recent years, little change was visible in the results for 2004. In the African and European regions, where high proportions of patients fail treatment or die, or are lost from DOTS cohorts, HIV/AIDS and MDR-TB are, respectively, major obstacles to TB control. But incomplete cohort data from these regions show that programme management also continues to be weak.
Clearly, NTPs must continue to improve case-finding and treatment success within the framework of the Global Plan, working towards the MDGs. To reach the targets of 70% case detection and 85% treatment success is a precondition for achieving a major impact with DOTS and the Stop TB Strategy.
Epidemiological trends and the impact of TB control
Our conclusion that incidence, prevalence and mortality were falling globally by 2005 is based on the best available evidence, but needs to be verified with more and better information. Current point estimates of the key epidemiological indicators are, for many countries, derived by mathematical and statistical modelling, and from weak or indirect evidence. For example, it is uncertain whether TB incidence rate is still increasing in subregion Africa – low HIV, given that HIV prevalence is thought to be in decline in this group of African countries (Figure 7).4 In the Region of the Americas, TB prevalence and death rates had already fallen by 2005 to about half the 1990 values, 10 years ahead of the 2015 target year. But this conclusion is not based on direct measurements of prevalence, and is guided by limited information about TB deaths (Annex 3). Moreover, the fall in case notifications has, for unknown reasons, slowed or reversed in recent years in some Latin American countries, including Brazil, Mexico and Peru.
The ultimate goal is to measure incidence through reliable case notifications, prevalence via well-designed prevalence surveys, and deaths by comprehensive vital registration (Table 4). Most countries cannot yet measure all key indicators, and there is much scope for improving and validating methods such as verbal autopsy for counting TB deaths in the population at large (i.e. outside DOTS cohorts).
Notwithstanding this cautious note on evaluation, the trend in TB incidence in some countries is clear and, in a few instances, the fall in TB can be attributed to the implementation of good control programmes. In 10 countries in the Eastern Mediterranean Region, for example, case notification rates were falling at 2–10% annually between 1994 and 2005. For the majority of these countries, the trends in case reports probably reflect the underlying trend in incidence. The higher rates of reduction (e.g. Jordan, Lebanon) are likely to reflect some impact of DOTS programmes, although the size of this impact is not easily quantified. New Caledonia is a more persuasive example, albeit on a small scale, of impact due to a good programme of drug treatment: the overall case notification rate fell at an average of 9% each year between 1990 and 2005.
In contrast, some countries are not showing the reductions in incidence expected after several years of DOTS implementation. Viet Nam has apparently had high and stable case detection and treatment success rates for a decade, and yet there are no indications that the total number of TB cases is falling. An examination of the notification trends by age and sex shows that case rates are falling among adults aged 35–64 years (especially women), but they are increasing among 15-24 year-olds (especially men) (Annex 2). In Figure 23 we have presented this phenomenon in another way: the average age of TB patients is falling among younger adults but increasing among the elderly. Such differences among and between younger and older adults can be seen in data from Bangladesh, China, Myanmar, Sri Lanka and Thailand. In Indonesia, exceptionally, the average age of older as well as younger TB patients is falling. In the United States of America, the average age is falling among younger men and women but not, apparently, among older people. Among people 15–54 years old in Morocco, the average age of women with TB is falling, but for men it is increasing.
This analysis, based only on surveillance data, is not powerful enough to determine the direction of the TB epidemics in these countries, or to fully explain the patterns of change with age. The observations do, however, help to refine the epidemiological questions. In particular, they underline the importance of understanding how the epidemiology of TB among young men and women could be slowing the decline of the epidemic in the established market economies, and in those Asian countries that have most of the world’s TB patients.
While the slow decline in TB incidence is a concern in Asia, any reduction in TB is welcome news in Africa. After more than a decade of rising case numbers, the increase in the case notification rate in eastern and southern African countries (Africa – high HIV) appears to have halted and may now be in decline. The upward shift in the average age of TB patients in Uganda and UR Tanzania is consistent with the flat or declining trend in case notifications, and follows the trend in HIV prevalence in these two countries. The stabilization or decline of TB in parts of sub-Saharan Africa is the main reason why the incidence rate has begun to fall globally.
Although incidence, prevalence and death rates now appear to be in decline, prevalence and death rates are not yet falling fast enough to achieve the MDGs globally by 2015. The decline will be accelerated by finding and curing more patients. The total number of patients diagnosed and treated in 2005 is in line with expectations for 2006, but the marked variations in case detection among WHO regions in 2005 will persist without remedial action. And there were major deficiencies in 2005 in the diagnosis and treatment of HIV-positive and MDR-TB patients, which are reflected in budgets for 2005–2007 (see Financing TB control). The present analysis leads to the conclusion that investment and implementation need to be stepped up especially, but not exclusively, in the African, Eastern Mediterranean and European regions.
1 Global tuberculosis control: surveillance, planning and financing. WHO report 2006. Geneva, World Health Organization, 2006 (WHO/HTM/TB/2006.362).
2 Lönnroth K et al. Public–private mix for DOTS implementation: what makes it work? Bulletin of the World Health Organization, 2004, 82:580–586.
3 Lönnroth K et al. Hard gains through soft contracts: productive engagement of private providers in tuberculosis control. Bulletin of the World Health Organization, 2006, 84:876–883.
4 AIDS epidemic update: December 2006. Geneva, UNAIDS/WHO, 2006.