Epidemiology in Developing Countries

Burden of Disease

While overall mortality rates, years of potential life lost, and life expectancy provide important insight into the health of a population, none provides information about quality of life. Rather, they are limited to information about quantity of life. Yet disabilities are important considerations when understanding population health. To this end, the World Bank funded the Burden of Disease Study, a collaborative effort of the World Health Organization and university researchers to describe the burden of disease for nations, incorporating both quantity of life and quality of life. The research also pulled together information on the major risk factors for each nation's burden of disease.

Burden of disease is estimated by combining information measured by years of potential life lost (YPLL) and years of healthy life lost due to disability (YLD). This combination of information forms disabilityadjusted life years (DALYs), which estimate the years of healthy life lost. For example, if a child dies of pneumoniaatage1, the child has 54 more years of YPLL compared to an individual who dies of pneumonia at age 55. Deaths in childhood have substantial impact on the measure of YPLL; thus, for countries with high childhood mortality, the YPLL and DALY are substantial per capita. Similarly, if an infectious disease, such as onchocerciasis (or ‘river blindness’), causes blindness of a 5-year-old, the YLD and DALY will be 39 years more than if the same disease causes blindness of a 44-year-old. Combining this information across all diseases in a country creates one summary measure for the country that provides a measure of health. The DALYs can also be computed by gender and for specific diseases and risk factors to understand their relative importance.

Approximately 58 million of the 6.5 billion people in the world died in 2006. Shockingly, about 20% of these deaths are children, disproportionately from developing countries. Developing countries also have substantial deaths in the adolescent age range, while wealthy countries carry a relatively high death rate among those in young and middle adulthood (ages 15 to 59 years). Infectious diseases, particularly respiratory and diarrheal diseases, maternal and perinatal conditions, and malnutrition, continue to play an important role in mortality for the people of developing countries. Malaria ravages sub-Saharan Africa, currently the second leading cause of death after HIV/AIDS in that region. Tuberculosis also is a growing cause of death and disability in developing countries worldwide, becoming increasingly lethal due to drug resistance and coinfection with HIV. However, many developing countries have undergone a key transition in mortality: With the exception of sub-Saharan Africa and South Asia, chronic diseases now outpace [Page 331]infectious diseases as the cause of death. Heart disease and cerebrovascular disease are now the leading causes of death. Injuries, including violence, occupationrelated injuries, falls, and traffic crashes, also take their toll in lives.

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