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GOAL AND TARGET ADDRESSED

Goal 6. Combat HIV/AIDS, malaria and other diseases Target 6.C. Have halted by 2015 and begun to reverse the incidence of malaria and other major diseases

DEFINITION AND METHOD OF COMPUTATION

Definition
The incidence of tuberculosis (TB) is defined as the number of new TB cases in one year per 100,000 population. The prevalence of tuberculosis is defined as the number of TB cases in a population at a given point in time (sometimes referred to as "point prevalence") per 100,000 population. Death rates associated with tuberculosis are defined as the estimated number of deaths due to TB in one year per 100,000 population.

Concepts
A tuberculosis case is defined as a patient in whom tuberculosis has been bacteriologically confirmed or diagnosed by a clinician.

Tuberculosis 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.

Method of computation
This indicator is calculated by dividing the calculated numbers of incidence, prevalence and deaths by the total population in units of 100,000 people. Population estimates are used where the only data available are data reported through the administration of health services. Total population in the survey is used when the data come from household surveys.

RATIONALE AND INTERPRETATION

Detecting tuberculosis and curing it are key interventions for addressing poverty and inequality. Prevalence and deaths are more sensitive markers of the changing burden of tuberculosis than incidence (new cases), but data on incidence are more comprehensive and give the best overview of the impact of global tuberculosis control.

Incidence rates are important because they give an indication of the extent of TB in a population, and of the size of the task faced by a national TB control programme. Incidence rates can be used to track changes in the rate at which people infected with Mycobacterium tuberculosis develop TB disease. Because TB can develop in people who became infected in the past, however, the effect of TB control on incidence is less visible than the effect on prevalence or death rates.

Prevalence and death rates can be used to directly monitor the burden of TB because they indicate the number of people suffering from the disease at a given point in time and the number dying each year. Prevalence and mortality rates are also useful for monitoring the effects of improvements in TB control because treatment reduces the average duration of the disease (thus decreasing prevalence) and the likelihood of dying from the disease.

SOURCES AND DATA COLLECTION

Available data sources differ from country to country, but generally include case notifications and death records (from routine surveillance and vital registration), and measures of the prevalence of disease (from population-based surveys). Prevalence of disease surveys are costly and logistically complex; however, 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. In addition, mortality surveys and demographic surveillance systems that use verbal autopsy to determine cause of death are a potential source of improved estimates of TB mortality. Surveys are particularly useful where routine surveillance data are poor.

The availability of direct measures of tuberculosis prevalence is increasing, with national surveys being implemented in around 20 TB-endemic countries between 2010 and 2015. Direct measures of the tuberculosis death rate come from vital statistics registration. Reliable figures require that death registration be nearly universal and that the cause of death be reported routinely on the death record and determined by a qualified observer according to the latest International Classification of Diseases. Such information is not available in many developing countries.

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 Multiple Indicator Cluster Surveys (MICS) or the Demographic and Health Surveys (DHS), although these usually refer only to children under five and do not provide death rates. Population data come directly or indirectly from population censuses.

DISAGGREGATION

Case notifications should be disaggregated by site of disease (pulmonary/extra-pulmonary), type of laboratory confirmation (usually sputum smear), and history of previous treatment.

New smear-positive cases can be disaggregated by age and sex. Many control programmes can also disaggregate cases according to the presence of drug resistance. The World Health Organization (WHO) recommends that recording and reporting programmes include disaggregation of notified cases by HIV status.

COMMENTS AND LIMITATIONS

Routine surveillance data provide a good basis for estimating incidence in countries where the majority of incident cases are treated and notified to WHO. But in most countries with a high burden of tuberculosis, incidence can only be estimated indirectly, usually with a large uncertainty. Nevertheless, where the proportion of cases notified is consistent over time (even if it is low), trends in notified cases can help assess trends in incidence. Where TB control efforts change over time it is difficult to differentiate between changes in incidence and changes in the proportion of cases notified.

GENDER EQUALITY ISSUES

At younger ages, the prevalence of disease is similar in boys and girls. At older ages, a higher prevalence has been found in men, and in most parts of the world, more men than women are diagnosed with tuberculosis and die from it. However, recent analyses comparing infection and disease rates suggest that the propensity to develop the disease after infection with Mycobacterium tuberculosis (the progression rate) may be greater among women of reproductive age than among men of the same age. A recent review of socio-economic and cultural factors relating to these suggested differences has called for further research to clarify such differences in the epidemiology of tuberculosis.

Although more men than women die of tuberculosis, the disease is still a leading cause of death from infectious diseases among women. Because tuberculosis affects women mainly in their economically and reproductively active years, the impact of the disease is also strongly felt by their children and families.

DATA FOR GLOBAL AND REGIONAL MONITORING

WHO is the international agency responsible for these indicators at the international level. Data are collected yearly through requests for information to the National Tuberculosis Control Programmes (NTPs) or other relevant public health authorities. A standardized online data collection website is used by all countries. 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. 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.

Online reports completed by countries are compiled and reviewed by WHO country offices, regional offices and headquarters. Feedback is then 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 WHO regional office and the European Centre for Disease Prevention and Control (ECDC). ECDC subsequently publishes an annual report with additional analyses, using more detailed data for the European Region.

Where population data 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.

Regional and global estimates are produced by aggregating national estimates, (i.e. to calculate the global incidence rate of TB per 100,000 population for a given year, TB incidence estimates for individual countries are summed and divided by the sum of the population of all countries multiplied by 100,000).

All estimates of TB burden (incidence, prevalence and mortality) are provided with uncertainty bounds.

SUPPLEMENTARY INFORMATION



EXAMPLES



REFERENCES

GUNN, S.W.A. (1990). Multilingual Dictionary of Disaster Medicine and International Relief. Kluwer Academic Publishers. Dordrecht, The Netherlands.

STOP TB PARTNERSHIP. Stop Tuberculosis, the Stop TB Partnership. Geneva. Internet site http://www.stoptb.org.

WORLD HEALTH ORGANIZATION (2011). Global Tuberculosis Control 20119: Epidemiology, Strategy, Financing. Geneva. Available from http://www.who.int/tb/publications/global_report/2011.

WORLD HEALTH ORGANIZATION (2009). International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10) . Geneva. Available from http://www.who.int/classifications/icd.

WORLD HEALTH ORGANIZATION (2010). The Global Plan to Stop TB, 2011–2015. Geneva. Available from http://www.stoptb.org/assets/documents/global/plan/TB_GlobalPlanToStopTB2011-2015.pdf

WORLD HEALTH ORGANIZATION (2006). The Stop TB Strategy: Building on and Enhancing DOTS to meet the TB-related Millennium Development Goals. Geneva. Available from http://www.who.int/tb/publications/2006/stop_tb_strategy.pdf.

WORLD HEALTH ORGANIZATION (annual). World Health Report. Geneva. Available from http://www.who.int/whr.

WORLD HEALTH ORGANIZATION. Global TB Database. Geneva. Internet site http://www.who.int/tb/country/data/download/en/index.html.

WORLD HEALTH ORGANIZATION. WHO Statistical Information System (WHOSIS) . Internet site http://www.who.int/whosis.

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