Incidence (cases arising in a given time period, usually one year) gives an indication of the burden of TB in a population, and of the size of the task faced by a national TB control programme. Incidence can change as the result of changes in transmission (the rate at which people become infected with Mycobacterium tuberculosis), or changes in the rate at which people infected with Mycobacterium tuberculosis develop TB disease (e.g. as a result of changes in nutritional status or of HIV infection). Because TB can develop in people who became infected many years previously, the effect of TB control on incidence is less rapid than the effect on prevalence or mortality. Target 6.c of the Millenium development Goals is to "have halted by 2015 and begun to reverse the incidence of malaria and other major diseases". Indicator 6.9 is defined as "incidence, prevalence and death rates associated with TB".

The estimated number of new and relapse tuberculosis (TB) cases arising in a given year. All forms of TB are included, including cases in people living with HIV. Published values are rounded to two significant figures. Uncertainty bounds are provided in addition to best estimates. See Annex 1 of the WHO global tuberculosis control report

HIV status

Impact

Estimates of TB incidence are produced through a consultative and analytical process led by WHO and are published annually. These estimates are based on annual case notifications, assessments of the quality and coverage of TB notification data, national surveys of the prevalence of TB disease and on information from death (vital) registration systems.   Estimates of incidence for each country are derived using one or more of the following approaches, depending on the available data:   1. incidence = case notifications / estimated proportion of cases detected   2. incidence = prevalence / duration of condition   3. incidence = deaths / proportion of incident cases that die   Uncertainty bounds are provided in addition to best estimates.   Details are available from  Policy and recommendations for how to assess the epidemiological burden of TB and the impact of TB control  and Annex 1 of the WHO global tuberculosis control report

Estimates are also produced at global level, for WHO regions and for World Bank Income Groups. For methodology, see Annex 1 of the WHO global tuberculosis control report  

Cases

3

Annual

Routine surveillance data provide a good basis for the estimate of incidence in countries where the majority of incident cases are treated and notified to WHO. Where the proportion of cases notified is consistent over time (even if it is low), trends in incidence can be judged from trends in notified cases. Where TB control efforts change over time it is difficult to differentiate between changes in incidence and changes in the proportion of cases notified. A national surveillance system is an integral part of good TB control, and one of the components of DOTS, which forms the core of the Stop TB Strategy. As surveillance improves in countries implementing the strategy, so will estimates of the incidence of TB.

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