Estimates of TB incidence are based on a consultative and analytical process led by WHO and are published annually (see reference 5). Estimates of incidence for each country are derived using one or more of four approaches, depending on the available data:

incidence = case notifications / estimated proportion of cases detected
incidence = prevalence / duration of condition
incidence = annual risk of TB infection x Stýblo coefficient
incidence = deaths / proportion of incident cases that die.

The Stýblo coefficient in equation (3) is taken to be a constant, with an empirically derived value in the range 40–60, relating risk of infection (% per year) to the incidence of sputum smear-positive cases (per 100 000 per year). Given two of the quantities in any of these equations, we can calculate the third, and these formulae can be rearranged to estimate incidence, prevalence and death rates. The available data differ from country to country but include case notifications and death records (from routine surveillance and vital registration), and measures of the prevalence of infection and disease (from population-based surveys).

For each country, estimates of incidence for each year during the period 1995–2004 have been made as follows. First a reference year is selected, for which there is a best estimate of incidence; this may be the year in which a survey was carried out, or the year for which incidence was first estimated. Then the series of case notifications is used to determine how incidence changed before and after that reference year. The time series of estimated incidence rates is constructed from the notification series in one of two ways: if the rate of change of incidence is roughly constant through time, an exponential trend is fitted to the notifications; if the rate varies through time (eastern Europe, central Europe and high-HIV Africa), a three-year moving average of the notification rates is used. If the notifications for any country are considered to be an unreliable guide to trend (e.g. because reporting effort is known to have changed; or because reports are clearly erratic, changing in a way that cannot be attributed to TB epidemiology), the aggregated trend for all other countries from the same epidemiological region that have reliable data is applied. For some countries (China, Indonesia and Nepal), the assessment of the trend in incidence is based on risk of infection derived from other sources (tuberculin surveys for China and Nepal; prevalence surveys for Indonesia). For those countries that have no reliable data from which to assess trends in incidence (e.g. for countries such as Iraq, for which data are hard to interpret) and which are atypical within their own regions, incidence is assumed to be stable.

Further details are available in the following references:

The Stop TB Strategy: building on and enhancing DOTS to meet the TB-related Millennium Development Goals. Geneva, World Health Organization, 2006 (WHO/HTM/STB/2006.37).
The Global Plan to Stop TB, 2006–2015. Geneva, World Health Organization, 2006 (WHO/HTM/STB/2006.35).
Dye C et al. Global burden of tuberculosis: estimated incidence, prevalence and mortality by country. Journal of the American Medical Association 1999, 282:677–686.
Corbett EL et al. The growing burden of tuberculosis: global trends and interactions with the HIV epidemic. Archives of Internal Medicine 2003, 163:1009–1021.
Global tuberculosis control: surveillance, planning, financing. WHO report 2008. Geneva, World Health Organization (WHO/HTM/TB/2008.393).
Dye C et al. Evolution of tuberculosis control and prospects for reducing tuberculosis incidence, prevalence, and deaths globally. Journal of the American Medical Association, 2005, 293:2767-2775.

The upper bound and lower bound values are the 95% confidence intervals of mid-point (best) estimates of TB incidence rate in a population of 100,000 in each year.

Project Countries

Marshall Islands

Comparisons

Country Indicators

Differences

Why is there a difference?

International

Country