Epidemiologic Transition

Epidemiology is the branch of medical science concerned with the incidence, distribution, and control of diseases that are prevalent among a population at a particular time and are produced by some special causes not generally present in the affected place.

The epidemiologic transition focuses on distinctive health threats in each stage of the demographic transition. Epidemiologists rely heavily on geographic concepts such as scale and connection because measures to control and prevent an epidemic derive from understanding its distinctive distribution and method of diffusion. The concept was originally formulated by epidemiologist Abdel Omran in 1971.

Stage 1: Pestilence & Famine

In stage 1 of the epidemiologic transition, epidemics and pandemics were principal causes of human deaths, along with accidents and attacks by animals and other humans. Malthus called these causes of deaths “natural checks” on the growth of the human population in stage 1 of the demographic transition. An epidemic is a widespread occurrence of an infectious disease in a community at a particular time. An epidemic affects many persons at the same time and spreads from person to person in a locality where the disease is not permanently prevalent. A pandemic is an epidemic that occurs over a wide geographic area and affects a very high proportion of the population at the same time.

History’s most violent stage 1 pandemic was the Black Plague (bubonic plague), which was probably transmitted to humans by fleas from migrating infected rats. About 25 million Europeans—at least one-half of the continent’s population—died between 1347 and 1350.

Stage 2: Receding Pandemics

Stage 2 of the epidemiologic transition is the stage of receding pandemics because improved sanitation, nutrition, and medicine during the Industrial Revolution reduced the spread of infectious diseases.

A century before the invention of computers, a mapping technique that anticipated GIS helped to explain and battle the stage 2 pandemic of cholera in nineteenth-century London. To understand cholera, Dr. John Snow (1813–1858), a British physician (not a geographer), created a hand-made GIS in 1854. On a map of London’s Soho neighborhood, Snow overlaid two other maps, one showing the addresses of cholera victims and the other the location of water pumps—which for the poor residents of Soho were the principal source of water for drinking, cleaning, and cooking

Stage 2 Disease: Dr. John Snow’s 1854 Cholera MAP of London

The overlay maps showed that cholera victims were not distributed uniformly through Soho, but rather were clustered around one pump on Broad Street. Tests at the Broad Street pump subsequently proved that the water there was contaminated by sewage. London’s poor were disproportionately affected by cholera because they were more likely to have to use contaminated water.

Death rates did not decline immediately during the Industrial Revolution. Poor people crowded into rapidly growing industrial cities had high death rates. Cholera—uncommon in rural areas—became an virulent epidemic in urban areas. Construction of water and sewer systems had eradicated cholera in Europe and North America by the late nineteenth century.

Cholera persists in several developing regions in stage 2 of the demographic transition, especially sub-Saharan Africa and South and Southeast Asia, where many people lack access to clean drinking water. Cholera is widespread in Yemen as a result of a civil war that has disrupted sanitation services, including provision of clean water and garbage pickup.

Stage 2 Disease: Cholera

(a) Cholera in Africa and southern Asia (b) Cholera in the Caribbean

Stage 3: Degenerative Diseases

Stage 3 of the epidemiologic transition is characterized by a decrease in deaths from infectious diseases and an increase in chronic disorders associated with aging. The two especially important chronic disorders in stage 3 are cardiovascular diseases, such as heart attacks, and various forms of cancer. The global pattern of cancer is the opposite of that for stage 2 diseases; sub-Saharan Africa and South Asia have the lowest incidence of cancer, primarily because of the relatively low life expectancy in those regions

Stage 4: Delayed Degenerative & Lifestyle Diseases

Omran’s epidemiologic transition was extended by S. Jay Olshansky and Brian Ault to stage 4, the stage of delayed degenerative diseases. The major degenerative causes of death—cardiovascular diseases and cancers—linger, but the life expectancy of older people is extended through medical advances. Through medicine, cancers spread more slowly or are removed altogether. Operations such as bypasses repair deficiencies in the cardiovascular system.

Some behavioral changes have improved health in stage 4 countries. These include better diet, reduced use of tobacco and alcohol, and more exercise. On the other hand, death rates have increased in stage 4 countries through use of prescription and illegal drugs, consumption of non-nutritious food, and sedentary behavior.

Increased deaths related to opioids have been especially challenging in stage 4 countries. As shown in Chapter 1, opioid-related deaths have not been distributed uniformly within the United States. Deaths are spatially associated with frequency of prescription of opioids.

Stage 4 Disease: Opioids, 2016

Pause & Reflect

Why do pandemics decline during stage 2 of the demographic transition?