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 prevalence refers to the number of cases of TB (all forms) in a population at a given point in time (sometimes referred to as "point prevalence"). It is expressed as the number of cases per 100,000 population. Estimates include cases of TB 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 prevalence are based on a consultative and analytical process led by WHO and are published annually. Details of the methods used to estimate TB prevalence are provided in the references, listed below.
Country-specific estimates of prevalence are, in most instances, derived from estimates of incidence (for additional details, please refer to the TB incidence indicator metadata) combined with assumptions about the duration of disease.
The prevalence of TB is calculated from the product of incidence and duration of disease:
Prevalence = incidence x duration of the condition.
The duration of disease is assumed to vary according to whether the disease is smear-positive or not; whether the individual receives treatment in a DOTS programme, a non-DOTS programme, or is not treated at all; and whether the individual is infected with HIV.
For more information please see the following:
Global TB database: www.who.int/tb/country/global_tb_database
Prevalence of disease surveys are costly and logistically complex, but they do provide a direct measure of bacteriologically confirmed, prevalent TB disease, and can serve as a platform for other investigations, e.g., the interactions between patients and the health system. Surveys are particularly useful where routine surveillance data are poor.
Direct measures of tuberculosis prevalence, which come from vital registration, are uncommon. Reliable figures require that death registration be nearly universal and that the cause of death be reported routinely on the death records and determined by a qualified observer according to the International Classification of Diseases. Such information is generally not available in developing counties. Vital statistics registration systems tend to underestimate tuberculosis deaths, although time series data from some countries in Asia and America give a useful indication of trends.
In the absence of direct measures of prevalence and death rates, a variety of techniques can be used to estimate these values. Administrative data are derived from the administration of health services. Data can also be obtained from household surveys such as the Multiple Indicator Cluster Surveys (MICS) or the Demographic Health Surveys, although they usually refer only to children under five or provide death rates.
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 www.eurotb.org
The details of estimation are described in publications in peer-reviewed journals 1,2,3. Because accurate measurement is crucial in the evaluation of epidemic trends, a recent paper provides methodological guidance4, 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).
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 TB prevalence is measured indirectly from TB incidence. For some countries, the TB prevalence is measured directly by TB prevalence surveys (see reference 3, 4 and 5-Annex 4, listed in “Method of Computation”).
WHO publishes data on case notifications 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 prevalence rate of TB per 100,000 population for a given year, the sum of the estimate of TB prevalence 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