The transition from high to low mortality and fertility that accompanied socioeconomic development has also meant a shift in the leading causes of disease and death. Demographers and epidemiologists describe this shift as part of an “epidemiologic transition” characterized by the waning of infectious and acute diseases and the emerging importance of chronic and degenerative diseases. High death rates from infectious diseases are commonly associated with the poverty, poor diets, and limited infrastructure found in developing countries. Although many developing countries still experience high child mortality from infectious and parasitic diseases, one of the major epidemiologic trends of the current century is the rise of chronic and degenerative diseases in countries throughout the world— regardless of income level.
Evidence from the multicountry Global Burden of Disease project and other international epidemiologic research shows that health problems associated with wealthy and aged populations affect a wide and expanding swath of world population. Over the next 10 to 15 years, people in every world region will suffer more death and disability from such noncommunicable diseases as heart disease, cancer, and diabetes than from infectious and parasitic diseases. The myth that noncommunicable diseases affect mainly affluent and aged populations was dispelled by the project, which combines information about mortality and morbidity from every world region to assess the total health burden from specific diseases. The burden is measured by estimating the loss of healthy years of life due to a specific cause based on detailed epidemiological information. In 2008, noncommunicable diseases accounted for an estimated 86 percent of the burden of disease in high-income countries, 65 percent in middle-income countries, and a surprising 37 percent in low-income countries.
Figure 6. The Increasing Burden of Chronic Noncommunicable Diseases: 2008 and 2030
Source: World Health Organization, Projections of Mortality and Burden of Disease, 2004-2030. Available at: http://www.who.int/healthinfo/global_burden_disease/projections/en/index.html .
By 2030, noncommunicable diseases are projected to account for more than one-half of the disease burden in low-income countries and more than three-fourths in middle-income countries. Infectious and parasitic diseases will account for 30 percent and 10 percent, respectively, in low- and middle-income countries (Figure 6). Among the 60-and-over population, noncommunicable diseases already account for more than 87 percent of the burden in low-, middle-, and high-income countries.
But the continuing health threats from communicable diseases for older people cannot be dismissed, either. Older people account for a growing share of the infectious disease burden in low-income countries. Infectious disease programs, including those for HIV/AIDS, often neglect older people and ignore the potential effects of population aging. Yet, antiretroviral therapy is enabling more people with HIV/AIDS to survive to older ages. And, there is growing evidence that older people are particularly susceptible to infectious diseases for a variety of reasons, including immunosenescence (the progressive deterioration of immune function with age) and frailty. Older people already suffering from one chronic or infectious disease are especially vulnerable to additional infectious diseases. For example, type 2 diabetes and tuberculosis are well- known “comorbid risk factors” that have serious health consequences for older people.