Epidemiological transition

In demography and medical geography, epidemiological transition is a phase of development witnessed by a sudden and stark increase in population growth rates brought by improved food security and innovations in public health and medicine, followed by a re-leveling of population growth due to subsequent declines in fertility rates. This accounts for the replacement of infectious diseases by chronic diseases over time due to increased life span as a result of improved health care and disease prevention. This theory was originally posited by Abdel Omran in 1971. In demography and medical geography, epidemiological transition is a phase of development witnessed by a sudden and stark increase in population growth rates brought by improved food security and innovations in public health and medicine, followed by a re-leveling of population growth due to subsequent declines in fertility rates. This accounts for the replacement of infectious diseases by chronic diseases over time due to increased life span as a result of improved health care and disease prevention. This theory was originally posited by Abdel Omran in 1971. Omran divided the epidemiological transition of mortality into three phases, in the last of which chronic diseases replace infection as the primary cause of death. These phases are: In 1998 Barrett et al proposed two additional phases in which cardiovascular diseases diminish as a cause of mortality due to changes in culture, lifestyle and diet, and diseases associated with aging increase in prevalence. In the final phase, disease is largely controlled for those with access to education and health care, but inequalities persist. The epidemiological transition occurs when a country undergoes the process of transitioning from developing nation to developed nation status. The developments of modern healthcare and medicine, such as antibiotics, drastically reduce infant mortality rates and extend average life expectancy which, coupled with subsequent declines in fertility rates, reflects a transition to chronic and degenerative diseases as more important causes of death. The theory of epidemiological transition uses patterns of health and disease as well as their forms of demographic, economical and sociological determinants and outcomes. In general human history, Omran's first phase occurs when human population sustains cyclic, low-growth, and mostly linear, up-and-down patterns associated with wars, famine, epidemic outbreaks, as well as small golden ages, and localized periods of 'prosperity'. In early pre-agricultural history, infant mortality rates were high and average life expectancy low. Today, life expectancy in developing countries remains relatively low, as in many Sub-Saharan African nations where it typically doesn't exceed 60 years of age. The second phase involves improved nutrition as a result of stable food production along with advances in medicine and the development of health care systems. Mortality in Western Europe and North America was halved during the 19th century due to closed sewage systems and clean water provided by public utilities, with a particular benefit for children of both sexes and to females in the adolescent and reproductive age periods, probably because the susceptibility of these groups to infectious and deficiency diseases is relatively high. An overall reduction in malnutrition enabled populations to better resist infectious disease. Treatment breakthroughs of importance included the initiation of vaccination during the early nineteenth century, and the discovery of penicillin in the mid 20th century, which led respectively to a widespread and dramatic decline in death rates from previously serious diseases such as smallpox and sepsis. Population growth rates surged in the 1950s, 1960's and 1970's to 1.8% per year and higher, with the world gaining 2 billion people between 1950 and the 1980s. A decline in mortality without a corresponding decline in fertility leads to a population pyramid assuming the shape of a bullet or a barrel, as young and middle-age groups comprise equivalent percentages of the population. Omran's third phase occurs when human birth rates drastically decline from highly positive replacement rates to stable replacement numbers. In several European nations replacement rates have even become negative. This transition generally represents the net effect of individual choices on family size and the ability to implement those choices. Omran gives three possible factors tending to encourage reduced fertility rates: Improvements in female and childhood survival that occur with the shift in health and disease patterns discussed above have distinct and seemingly contradictory effects on fertility. While better health and greater longevity enjoyed by females of reproductive age tend to enhance fertility, the reduced risks to infants and young children that occurs in the later stages of the transition tends to have the opposite effect: prolonged breastfeeding associated with reduced mortality among infants and toddlers, together with parental recognition of improved childhood survival, tend to lengthen birth intervals and depress overall reproductive rates.