INTRODUCTION Estimates of the burden of disease caused by TB and measured in terms of incidence, prevalence and mortality are produced annually by WHO using information gathered through surveillance systems (case notifications and death registrations), special studies (including surveys of the prevalence of disease), mortality surveys, surveys of under-reporting of detected TB and in-depth analysis of surveillance data, expert opinion and consultations with countries. This document provides case definitions and describes the methods used in Global TB Report 2015 to derive TB incidence, prevalence and mortality. DEFINITIONS INCIDENCE is defined as the number of new and recurrent (relapse) episodes of TB (all forms) occurring in a given year. Recurrent episodes are defined as a new episode of TB in people who have had TB in the past and for whom there was bacteriological confirmation of cure and/or documentation that treatment was completed. In the remainder of this technical document, relapse cases are referred to as recurrent cases because the term is more useful when explaining the estimation of TB incidence. Recurrent cases may be true relapses or a new episode of TB caused by reinfection. In current case definitions, both relapse cases and patients who require a change in treatment are called _retreatment cases_. However, people with a continuing episode of TB that requires a treatment change are prevalent cases, not incident cases. PREVALENCE is defined as the number of TB cases (all forms) at a given point in time. MORTALITY from TB is defined as the number of deaths caused by TB in HIV-negative people occurring in a given year, according to the latest revision of the International classification of diseases (ICD-10). TB deaths among HIV-positive people are classified as HIV deaths in ICD-10. For this reason, estimates of deaths from TB in HIV-positive people are presented separately from those in HIV-negative people. The CASE FATALITY RATE is the risk of death from TB among people with active TB disease. The CASE NOTIFICATION rate refers to new and recurrent episodes of TB notified to WHO for a given year. The case notification rate for new and recurrent TB is important in the estimation of TB incidence. In some countries, however, information on treatment history may be missing for some cases. Patients reported in the _unknown history_ category are considered incident TB episodes (new or recurrent). REGIONAL ANALYSES are generally undertaken for the six WHO regions (that is, 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). For analyses related to MDR-TB, nine epidemiological regions were defined (Figure [fig:epiregions]). These were African countries with high HIV prevalence, African countries with low HIV prevalence, Central Europe, Eastern Europe, high-income countries, Latin America, the Eastern Mediterranean Region (excluding high-income countries), the South-East Asia Region (excluding high-income countries) and the Western Pacific Region (excluding high-income countries).
Each year, new data become available for the estimation of TB disease burden. Periodically, methods for using surveillance and survey data as well as other sources of information to estimate TB disease burden are reviewed and updated. This box provides a summary of updates that were made in 2014. Updates for specific countries that are expected in the near future, pending the finalization of results from ongoing national prevalence surveys, are also highlighted. UPDATES IN THIS REPORT Updates based on new data from national TB prevalence surveys By August 2015, final results became available from national TB prevalence surveys implemented between 2012 and 2014 in Ghana, Malawi, Soudan, the Republic of Tanzania, Zambia and Zimbabwe. In Indonesia, burden estimates have been revised upwards (see Box a _FIX REFERENCE_). Given the size of Indonesia’s population and TB burden, this upward revision in burden estimates affects global estimates of the absolute number of TB cases and to a lesser extent TB deaths, but not overall trends. In the other 5 countries with new prevalence survey results, updated estimates are either higher (Ghana, Malawi, Zambia) or lower (Sudan, Zimbabwe) than previous estimates, with overlap in uncertainty intervals except for Malawi. Prevalence surveys result in estimates of prevalence that are generally more precise and more accurate than previous estimates indirectly derived from estimated incidence and heavily influenced by expert-opinion (see Figure 1). Details are provided in the ONLINE TECHNICAL APPENDIX.
BACKGROUND AND METHODS A national case-based internet-based TB notification system is a key element of Korea’s TB control programme, linked to the initiation of response measures including outbreak investigations, evaluation of contacts and TB case management. The online TB reporting system was established in 2000 . All TB patients who are treated in public health centers are notified to the Korea National TB Surveillance System (KNTSS). In 2006, a national survey found that only 67.6% of patients diagnosed and treated in the private sector were notified, despite a legal framework making notification of TB cases mandatory. Since 2008, the coverage of routine TB surveillance has been systematically assessed using record-linkage of medical records from the National Health Insurance (NHI) and records from the KNTSS database. National identification numbers are used for record-linkage. RESULTS Under-reporting of TB case notifications over 2012-2013 are presented in the table below. Under-reporting was defined as failing to report within 6 months.