Stop TB Department
World Health Organization
Postal Address:Avenue Appia, CH-1211 Geneva 27, Switzerland
Telephone: (+44) 22 791 1028
Fax: (1-514) 22 791 1589
Tuberculosis incidence is the estimated number of new tuberculosis (TB) cases arising in one year per 100,000 population. All forms of TB are included, as are cases in people with HIV.
TB is an infectious bacterial disease caused by Mycobacterium tuberculosis, which most commonly affects the lungs. It is transmitted from person to person via droplets from the throat and lungs of people with the active respiratory disease. In healthy people, infection with Mycobacterium tuberculosis often causes no symptoms, since the person's immune system acts to “wall off” the bacteria. The symptoms of active TB of the lung are coughing, sometimes with sputum or blood, chest pains, weakness, weight loss, fever and night sweats. Tuberculosis is treatable with a six-month course of antibiotics.
Human Immunodeficiency Virus (HIV) is a virus that weakens the immune system, ultimately leading to AIDS, the acquired immunodeficiency syndrome. HIV destroys the body’s ability to fight off infection and disease, which can ultimately lead to death.
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:
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 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.
Routine surveillance data provide a good basis for estimating 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 TB incidence.
Prevalence and death rates are more sensitive markers to the changing burden of tuberculosis than incidence (new cases), although data on trends in incidence are for more comprehensive and give the best overview of the incidence of tuberculosis control.
Where population sizes are needed to calculate TB indicators, the latest United Nations Population Division estimates are used. These estimates sometimes differ from those made by the countries themselves, some of which are based on more recent census data. The estimates of some TB indicators, such as the case detection rate, are derived from data and calculations that use only rates per capita, and discrepancies in population sizes do not affect these indicators. Where rates per capita are used as a basis for calculating numbers of TB cases, these discrepancies sometimes make a difference.
A standardized data collection form is distributed to all countries on an annual basis. Estimates are made using these data as well as country-specific analyses of TB epidemiology based on the published literature and consultation with national and international experts.
Every year, WHO requests information from the National Tuberculosis Control Programmes (NTPs) or relevant public health authorities. NTPs that respond to WHO are also asked to update information for earlier years where possible. As a result of such revisions, the data (case notifications, treatment outcomes, etc.) presented for a given year may differ from those published previously.
Completed forms are collected and reviewed at all levels of WHO, by country offices, regional offices and at headquarters. An acknowledgement form that tabulates all submitted data is sent back to the NTP correspondent in order to complete any missing responses and to resolve any inconsistencies. Then, using the complete set of data for each country, a profile is constructed that tabulates all key indicators, including epidemiological and financial data and estimates, and this too is returned to each NTP for review. In the WHO European Region only, data collection and verification are performed jointly by the regional office and a WHO collaborating centre, EuroTB (Paris). EuroTB subsequently publishes an annual report with additional analyses, using more detailed data for the European Region (
Because accurate measurement is crucial in the evaluation of epidemic trends, a recent paper provides methodological guidance based on a review by the WHO Task Force on TB Impact Measurement. This paper can be read in conjunction with the list of countries that have done, or are planning, infection (tuberculin) and disease prevalence surveys, and with the set of countries that now register deaths by cause and provide these data to WHO (including TB).
Dye et al. Measuring tuberculosis burden, trends and the impact of control programmes. Lancet Infectious Diseases (published online 16 January 2008).
Estimates made for all indicators and for all countries. See “Process of Obtaining Data”, above, for details.
Data are available for 212 countries and territories.
Estimates of TB incidence, prevalence and deaths are based on a consultative and analytical process. They are revised annually to reflect new information gathered through surveillance (case notifications and death registrations) and from special studies (including surveys of the prevalence of infection and disease).
For most countries, the case notification data reported by the countries and adjusted by WHO for the comprehensiveness of the TB surveillance system are used to calculate the TB incidence. The notification data were reported to WHO from 202 (out of 212) countries or territories for year 2006. However, for some countries, the estimate of incidence is measured indirectly from the estimate of TB prevalence or mortality measured by the TB prevalence surveys or the vital registration systems (see reference 3, 4 and 5-Annex 4, listed in “Method of Computation”).
The data on case notifications are published by WHO two years after diagnosis and three years after completion of treatment of TB cases.
Regional and global estimates are produced by aggregating national estimates, (e.g. to calculate the global incidence rate of TB per year per 100,000 population for a given year, the sum of estimate of TB incidence for individual countries is divided by the sum of the population of all countries multiplied by 100,000).
The WHO regions are the African Region, the Region of the Americas, the Eastern Mediterranean Region, the European Region, the South-East Asia Region and the Western Pacific Region. All essential statistics are summarized for each of these regions and globally. However, to make clear the differences in epidemiological trends within regions, the African Region is divided into countries with low and high rates of HIV infection (“high” is an infection rate of =4%, as estimated by UNAIDS in 2007). Central Europe is divided from Eastern Europe (countries of the former Soviet states plus Bulgaria and Romania), and Western European countries are combined with the other high-income countries.
Estimates are published annually, in March, are available in WHO’s Global TB Database at