Acute and Chronic Diseases

Historically the modal cause of death is disease. Diseases, also referred to as morbidities, are commonly classified into two categories: acute illness and chronic illness. Acute illness is characterized by sudden onset of symptoms and a brief duration. Examples include influenza and chicken pox. Most infectious diseases fall into this category. Acute illness may resolve on its own, may be treated with medications, or, in severe cases, may result in death. By contrast, chronic illness has a gradual onset of symptoms and an extended course. These types of illnesses usually result from degenerative conditions, traumas, lifestyle factors, or exposure to harmful environmental agents. Examples include diabetes, Alzheimer's disease, cancer, and most forms of heart disease. Although chronic illnesses are generally not curable, in many cases the sequelae of chronic conditions can be managed behaviorally or through medical intervention.

In 1900, the major causes of mortality in the United States were infectious diseases. The three leading causes of death were pneumonia and influenza, tuberculosis, and diarrheal diseases, respectively. The life expectancy at birth, in 1900, was 47.3 years; in contrast, a baby born in 2005 has a life expectancy of 77.8 years, an increase of more than 30 years. Much of the increase in life expectancy can be contributed to the changes in the major causes of mortality, with the leading causes of mortality shifting from acute illness to chronic illness.

In the United States and other more developed countries, acute illnesses have historically been important causes of death and have produced dramatic fluctuations in mortality; the Spanish flu epidemic of 1918 is one important example. More recently, however, with the life expectancy at birth reaching approximately 75 years for men and over 80 years for women, the primary source of death has shifted to chronic illness, especially heart disease and cancer. This entry summarizes the most common fatal chronic and acute illnesses in the United States, describes the historical shift from acute to chronic illnesses as the primary causes of death (epidemiological transition), and compares the level of chronic and acute illness in the United States to levels observed in other parts of the world.

Acute and Chronic Illness in the United States

According to a recent report by the National Center for Health Statistics, “Deaths: Final Data for 2005,” there were 2,448,017 recorded deaths in the United States in 2005, resulting in a crude death rate of 825.9 deaths per 100,000 population. A more detailed view of recent mortality in the U.S. population can be obtained by examining specific causes of death. The 15 leading causes of death are shown in Table 1. Of the major causes of mortality in the United States, most are chronic in nature. The two major causes of death on this list—heart disease and cancer—accounted for almost half of all deaths (49.4#x0025;) in 2005, providing compelling testament to the monolithic role that chronic disease currently plays as a cause of mortality.