Methods: Monitoring the detection and treatment of TB cases
Calculation of indicators
Following the 1991 World Health Assembly resolution, the main indicators which we use to measure progress in TB control are detection of infectious TB cases (target 70%) and successful treatment of such cases (target 85%). Because WHO urges worldwide implementation of the DOTS strategy, this report focuses on case detection and treatment success under DOTS.
Estimation of TB incidence
To calculate the case detection rate, we estimate TB incidence for every country in the world. Our estimates are based on a consultative and analytical process described elsewhere, and have been regularly updated since 1997.7,8 The approach to estimating incidence (the number of new cases in a given year, and the trend) is not the same for all countries and regions, but rather depends on the direct and indirect evidence available (e.g. surveys of the prevalence of infection and disease, vital registration data, quality of the surveillance system).
In all calculations of TB indicators, we use population estimates provided by the UN Population Division,9 even though they sometimes differ from estimates made by the countries themselves (some of which are based on more recent survey data). Where estimates of TB indicators, such as the case detection rate, are based on data and calculations that work with rates per capita, discrepancies in population estimates do not affect the indicators. Where rates per capita are used as a basis for calculating numbers of TB cases, these discrepancies sometimes do make a difference. Some examples of important differences are given in the country notes in Annex 2.
7 Dye C, Scheele S, Dolin P, Pathania V, Raviglione MC, Global burden of tuberculosis: estimated incidence, prevalence and mortality by country. Journal of the American Medical Association 1999; 282: 677 686.
8 Corbett EL, Watt C, Walker N, Maher D, Raviglione MC, Williams BG, Dye C. The growing burden of tuberculosis: global trends and interactions with the HIV epidemic. Archives of Internal Medicine 2003; 163: 1009–1021.
9 United Nations Population Division. World Population Prospects – the 2002 revision. New York, 2003.