Academic journal article Bulletin of the World Health Organization

Global Tuberculosis Incidence and Mortality during 1990-2000

Academic journal article Bulletin of the World Health Organization

Global Tuberculosis Incidence and Mortality during 1990-2000

Article excerpt

Estimates of tuberculosis incidence in 1990 for the developing countries by Murray (1) were extended by Sudre (2) to include the industrialized countries. Both authors used estimates of the annual risk of infection (ARI) in developing countries(a) to calculate the expected incidence. The present study forecasts the future global and regional burden of tuberculosis morbidity and mortality using tuberculosis notification data (i.e., cases reported to the Ministries of Health) to complement the ARI-based calculations. This dual approach was used to provide a separate set of estimates from those based on ARI data alone.

The impact of demographic factors (such as global population growth and aging of the world's populations) and epidemiological factors (such as adverse effects of the human immunodeficiency virus (HIV) epidemic and the beneficial effects of intervention programmes) is discussed.

Methods

Tuberculosis incidence

In 1990. WHO routinely collects data on the number of tuberculosis cases in Member States each year.(b) Within each WHO region, except the African region, an overall regional crude incidence rate was calculated by estimating the incidence in the most populated countries. Notification data were considered reliable when provided by programmes with an established surveillance system. Reliable notification data were preferentially used for these estimates. For countries with unreliable notification data, the annual risk of infection was used to estimate incidence. Notification data are relatively poor for the African region (sub-Saharan Africa), so a slightly different approach was used; the region was divided into four geographical areas and within each area, a crude incidence rate was estimated, based on the most reliable notification data (e.g., United Republic of Tanzania for East Africa, South Africa for southern Africa, Cote d'Ivoire for West Africa).

This approach differs from previous estimates of the 1990 incidence (1, 2), which were based solely on annual risk-of-infection data(a) and gave equal consideration to data from countries with different population sizes. While notification data are of poor quality for many countries, and any estimates based on such data will risk underestimating the incidence, reliable data are available from other countries, particularly those where good tuberculosis control programmes are established. The estimates presented in this paper must be considered conservative owing to the fact that tuberculosis cases are generally underreported.

In 1995 and 2000. In estimating future incidence, allowances were made for demographic factors (changes in the size and age structure of regional populations) and epidemiological factors (changes in underlying incidence rates). To accurately allow for both demographic and epidemiological factors, regional age-specific incidence rates for the years 1995 and 2000 were estimated and then applied to regional age-specific population projections for 1995 and 2000.

This was undertaken in two steps. First, data available at WHO on the age distribution of notified cases in each region during 1990 were applied to the 1990 regional crude incidence rates to derive the 1990 regional age-specific incidence rates. Second, trends in regional notification rates during 1985-90 were applied to the 1990 regional age-specific incidence rates to derive estimates of regional age-specific incidence rates for the years 1995 and 2000. This assumes that future age-specific trends will remain unchanged. These rates were then applied to regional age-specific population projections (3) to calculate the number of incident cases expected in 1995 and 2000. A more detailed description of these methods is reviewed elsewhere.(c)

Mortality in 1990, 1995 and 2000

Published case-fatality rates of 7% for industrialized countries (4) and reported rates of 15% for Eastern Europe were used. …

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