WHO report 2008
Global tuberculosis control
1.3 TB incidence in 2006 and trends since 1990
1.3.1 Estimated incidence in 2006
Based on surveillance and survey data (Annex 3; Annex 4), we estimate that 9.2 million new cases of TB occurred in 2006 (139 per 100 000), including 4.1 million (62 per 100 000) new smear-positive cases (Table 1.2; Figure 1.1). These numbers included TB in HIV-positive people. India, China, Indonesia, South Africa and Nigeria rank first to fifth in terms of incident cases; the estimated numbers of cases in these and other HBCs in 2006 are also shown in Table 1.2. Asia (South-East Asia and Western Pacific regions) accounts for 55% of global cases, and Africa accounts for 31%; the other three regions account for relatively small fractions of global cases.
Among the 9.2 million new cases of TB in 2006, we estimate that around 709 000 (7.7%) were HIV-positive. This estimate is based on the global estimates of HIV prevalence among the general population (all ages) published by the Joint United Nations Programme on HIV/AIDS (UNAIDS) and WHO in December 2007,1 as well as data on the relative risk of developing TB in HIV-positive and HIV-negative people (see Annex 2 for further details on methods). As in previous years, the African Region accounts for most HIV-positive cases: 85% in 2006 (Figure 1.2). Most of the remaining cases (6%) are in the South-East Asia Region, mainly in India. Some African countries account for a strikingly large number of cases relative to their population. South Africa, for example, has 0.7% of the world’s population but 28% of the global number of HIV-positive TB cases and 33% of HIV-positive cases in the African Region.
The magnitude of the TB burden within countries can also be expressed as the number of incident cases per 100 000 population (Figure 1.3). Among the 15 countries with the highest estimated TB incidence rates, 12 are in Africa (Figure 1.4). The high incidence rates estimated for the African countries in this list are partly explained by the relatively high rates of HIV coinfection. Where HIV infection rates are higher in adult populations, they are also estimated to be higher among new TB patients (Figure 1.4). Figure 1.5 maps the distribution of HIV among TB patients, showing the relatively high rates in countries of eastern and southern Africa.
1.3.2 Trends in incidence
The estimated average change in TB incidence (all forms) per 100 000 population over the 10-year period 1997–2006, based on case notifications reported by 134 countries that were judged to have a reliable series of data, was between –10% and +10% in all countries except for New Caledonia (Figure 1.6). Data from 93 countries indicate that incidence per capita was falling, albeit slowly; in 66 of these 93 countries the rate of decline was between zero and 6% per year.
By using estimates of the proportion of cases detected in each country, and by matching countries without trend data to those with such data, we can build a picture of incidence trends (all forms of TB) for nine epidemiologically different subregions of the world for the 17-year period 1990–2006 (Figure 1.7). The global incidence of TB per capita peaked around 2003 and appears to have stabilized or begun to decline. Incidence per 100 000 population is approximately stable in the European Region and is falling in all the five other WHO regions. It is also falling in all nine subregions, with the possible exception of African countries with low HIV prevalence (Africa – low HIV). The downward trend was fastest in the Latin America and Caribbean subregion (–3.4% per year, 2001–2006).
Globally, the slow decline in incidence per capita is more than offset by population growth. This means that the number of new cases was still increasing between 2005 and 2006, from 9.1 to 9.2 million (an increase of 0.6%). The increases in numbers of new cases were in the African, Eastern Mediterranean, European and South-East Asia regions.
In subregion Africa – high HIV, the annual change in TB incidence runs almost parallel with the change in HIV prevalence in the general population. Since 1990, both HIV prevalence and TB incidence have been increasing more slowly each year and, by 2006, both indicators were falling (Figure 1.8). The correspondence between declining HIV prevalence in the general population and reported TB cases is especially close in data from Malawi, the United Republic of Tanzania and Zimbabwe (data not shown).
1 2007 AIDS epidemic update. Geneva, Joint United Nations Programme on HIV/AIDS and World Health Organization, 2007 (UNAIDS/07.27E/JC1322E).