MDR-TB Treatment & Prevention
TB Impact Measurement: Policy and recommendations for how to assess the epidemiological burden of TB and the impact of TB control
Global targets for reducing the epidemiological burden of tuberculosis (TB) – measured as incidence, prevalence and mortality – have been set for 2015 within the context of the Millennium Development Goals (MDGs) and by the Stop TB Partnership. The targets are that the TB incidence rate should be falling globally by 2015 and that TB prevalence and death rates should be halved by 2015 compared with their levels in 1990. Achieving these impact targets is the focus of national and international efforts to control TB, and demonstrating whether or not they are achieved is of major importance for individual countries, the United Nations, the Stop TB Partnership and a variety of technical, financial and development agencies. A Global Task Force on TB Impact Measurement was established in June 2006. The Task Force is convened by the Stop TB Department of the World Health Organization (WHO), and includes international experts in TB epidemiology, representatives from countries with a high burden of TB, and representatives from a range of technical and financial agencies. The Task Force has a three-fold mandate:
• To produce a robust, rigorous and widely-endorsed assessment of whether the 2015 impact targets are achieved at global level, for each WHO region and in individual countries;
• To regularly report on progress towards the 2015 impact targets in the years leading up to 2015; and
• To strengthen national capacity in monitoring and evaluation of TB control.
This policy paper sets out WHO policies and recommendations for how TB incidence, prevalence and mortality should be measured in the years up to 2015. Many of these policies and recommendations will apply after 2015. The paper is based on policies and recommendations agreed by the WHO Global Task Force on TB Impact Measurement, which have also been endorsed by WHO’s Strategic and Technical Advisory Group for TB (STAG-TB). The major policies and related recommendations are as follows:
• Measuring TB incidence and TB mortality requires periodic analysis of the reliability and coverage of TB notification and vital registration data. The Task Force has developed a standard framework and related analyses and tools for this purpose. The framework has three major components: 1) assessment of data quality; 2) assessment of the extent to which time-series of notification and vital registration data provide a good proxy for trends in TB incidence and mortality, respectively; and 3) assessment of the fraction of all incident cases and deaths from TB that are recorded in surveillance data. Application of this framework should also be used to define recommendations for how national surveillance systems need to be strengthened, to progress towards the ultimate goal of measuring TB burden directly from notification and vital registration data, and to update estimates of disease burden;
• Surveys of the prevalence of TB disease should be implemented in at least 21 global focus countries. At least one survey should be implemented in these countries before 2015, and the Task Force will make special efforts to provide the necessary technical guidance and support. There are a further 32 countries that meet Task Force criteria for implementing a prevalence survey, but in most cases it will not be possible for the Task Force to provide intensive guidance and support. All surveys should follow WHO guidelines published in 2007 and related Task Force recommendations. For countries where surveys are not implemented, TB prevalence will need to be measured indirectly from estimates of TB incidence and the average duration of disease;
• Surveys of the annual risk of infection, which have been used in the past to estimate TB incidence, are no longer recommended;
• The Task Force will periodically review and update the data, assumptions and analytical methods used to translate surveillance and survey data into the estimates of TB incidence, prevalence and mortality that are published annually by WHO;
• The impact of TB control on changes in TB incidence, prevalence and mortality needs to be evaluated in more countries.
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