(The FASEB Journal. 2005;19:892-897.)
© 2005 FASEB
The epidemiological revolution of the 20th century
Silvio De Flora*,1,
Alberto Quaglia#,
Carlo Bennicelli* and
Marina Vercelli*,#
* Department of Health Sciences, University of Genoa, Italy; and
# Descriptive Epidemiology Unit, National Cancer Research Institute, Genoa, Italy
1Correspondence: Department of Health Sciences, University of Genoa, Via A. Pastore 1, I–16132 Genoa, Italy. E-mail: sdf{at}unige.it
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ABSTRACT
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Until 100 years ago the epidemiological scenario of human diseases had substantially remained unchanged. The 20th century has been characterized by a fantastic advance in life expectancy and by a shift from infectious to chronic degenerative diseases as prevailing causes of death. As an example of the epidemiological revolution in a developed country, we reconstructed, year by year from 1901 to 2000, the situation in Italy. Reference to the situation in other countries is also made. Both crude and age-adjusted mortality data were made available for males and females. A new turning point became evident in the second half of the 20th century with the decline of mortality for cardiovascular diseases and, more recently, for tumors. This review discusses the roots and rationale for these epidemiological changes. The discoveries made in the area of biomedical sciences, the progress in preventive and curative medicine, and the improvement of hygienic conditions have been so spectacular that 1 million lives are saved every year in Italy as compared with the late 19th century.—De Flora, S., Quaglia, A., Bennicelli, C., Vercelli, M. The epidemiological revolution of the 20th century.
Key Words: descriptive epidemiology • cardiovascular diseases • tumors • infectious diseases
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INTRODUCTION
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UNTIL RECENTLY, the epidemiological course of human diseases had substantially remained unchanged over many centuries and perhaps millennia. Life expectancy at birth was 20 years in prehistory, 30 at the beginning of the Christian era, and 35 by mid-19th century. However, during the last decades of the 19th century and throughout the 20th century, there was a breakthrough in biomedical sciences and environmental hygiene that revolutionized the epidemiological scenario in developed countries and, to a certain extent, in developing countries.
The focus of this review article is to document and analyze the changes that occurred during the past century in Italy, taking into account the progressive aging of the population, as a model and "state of the nation" for different countries. As reported and discussed below, there was a tremendous advance in life expectancy at birth, accompanied by a shift from infectious diseases to chronic degenerative diseases as prevailing causes of death in the population. Actually, the distinction between infectious diseases and degenerative diseases is not clear-cut, and the same is true for diseases related to accidental causes. In fact, it is well recognized that certain viral and bacterial chronic infections or parasitic diseases as well as repeated mechanical injuries may be involved in the pathogenesis of chronic degenerative diseases. This concept is taken into account in the International Classification of Diseases (ICD), in which infectious diseases and degenerative conditions are often categorized within the same family. Formalized for the first time in 1893 as the Bentillon Classification or International List of Causes of Death, the ICD underwent 10 revisions during the 20th century, in 1900 (ICD-1), 1909 (ICD-2), 1920 (ICD-3), 1929 (ICD-4), 1938 (ICD-5), and 1948 (ICD-6), when it was extended to include nonfatal diseases, then in 1955 (ICD-7), 1965 (ICD-8), 1975 (ICD-9), and 1989 (ICD-10) (ref 1
; http://www.wolfbane.com/icd).
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THE CROSSOVER OF MORTALITY CURVES DURING THE 20TH CENTURY
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As an example of the epidemiological trends occurring in a developed country during the 20th century, we reconstructed the dynamic course of the main pathological conditions and accidents responsible for death in the Italian population, year by year, from 1901 to 2000. Figure 1
and Fig. 2
report specific mortality curves based on crude data and age-adjusted data, respectively. General mortality and natality data for the whole population and separately for males and females are shown in Fig. 3
.
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Figure 1. Mortality rates (crude data) in Italy from 1901 to 2000, year by year, for the main diseases responsible for death in the population. The reported diseases include infectious and parasitic diseases (INF), malignant tumors (TUM), cardiovascular diseases (CARD), cerebrovascular diseases (CER), respiratory diseases, including influenza (RESP), digestive system diseases (DIG), and accidents (ACC). See text for the ICD-10 categories of diseases included in the analysis and other details.
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Figure 2. Mortality rates (age-adjusted data) in Italy from 1901 to 2000, year by year, for the main diseases responsible for death in the population. The reported diseases include infectious and parasitic diseases (INF), malignant tumors (TUM), cardiovascular diseases (CARD), cerebrovascular diseases (CER), respiratory diseases, including influenza (RESP), digestive system diseases (DIG), and accidents (ACC). See text for the ICD-10 categories of diseases included in the analysis and for the procedure used for age adjustment.
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Figure 3. Live birth rates and death rates for all causes, either crude or age adjusted, in Italy from 1901 to 2000, year by year
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The reported crude mortality rates are based on death certificates relative to the total Italian population and are normalized to 100,000 residents. Therefore, they may be affected by a variety of inaccuracies that typically characterize this source of data (2)
. Mortality rates per 100,000 were age adjusted using the world population as a standard through the direct method. The resident Italian population was used as denominator (3)
. The mortality curves shown in Figs. 1
and 2
refer to infectious and parasitic diseases (categories A00–B99 according to ICD-10), malignant tumors (C00–D09), cardiovascular diseases (I00-I52; I70-I99), cerebrovascular diseases (I60-I69), respiratory diseases, including influenza (J00–J99), digestive system diseases (K00–K93), and accidents (V01–Y98). Mortality values from 1901 to 1950 were inferred from ISTAT (4)
. Mortality values from 1951 to 2000 were obtained from the database of the Word Health Organization Mortality Information System (WHOSIS) (http://www3.who.int/whosis). The frequent revisions of ICD and other contingent situations forced us to make some adjustments to render the data more comparable and homogeneous with time. For instance, until 1967 (when ICD-8 was adopted in Italy), cerebrovascular diseases were included in the family of nervous system diseases and thereafter within the circulatory system diseases. Other adjustments were needed for infectious and digestive diseases, since until 1967 gastroenteritis and colitis were included within digestive system diseases; after adoption of ICD-8, they were classified as infectious diseases.
Figure 1
shows at a glance the epidemiological revolution of the 20th century. At the beginning of that century, the main causes of death were represented by diseases of the respiratory and digestive systems and by other infectious and parasitic diseases. Thereafter, there was a marked trend toward a decline of mortality from these diseases, although it should be kept in mind that death certificates often underestimate the real burden of infectious diseases. By mid-century there was an intricate crossover of mortality curves. Cardiovascular and cerebrovascular diseases, altogether, became the first causes of death in the early 1930s, and tumors became the second cause only at the beginning of the 1950s. Overall, these two families of chronic degenerative diseases grew until they were responsible for more than 70% of all deaths. However, even when considering crude mortality data (Fig. 1)
, especially in males, the number of deaths from chronic diseases started to decline in the last decades, as discussed below in more detail.
Besides these general trends, the observation of Figs. 1
and 3
highlight some evident peaks of mortality for all causes and specific diseases or accidental causes. For instance, the impressive mortality peak recorded in 1918 in males and females corresponds to the "Spanish flu" pandemic, the most devastating recorded outbreak of human diseases (5)
. As shown in Fig. 1
, in 1918 it Italy there was an excess of mortality for respiratory diseases of 
1000 per 100,000. The peak corresponding to the World War II period is underestimated, and the excess mortality during World War I is not detectable among accidental causes because most deaths were classified under "unknown causes," often with no indication of age. However, the mortality peaks recorded during the periods of the two world wars are well evident in Fig. 3
, along with the strong depression in natality rates (Fig. 3)
. Other mortality peaks recorded in accidental causes (Fig. 1)
are due to severe earthquakes that hit Italy in 1908 (Calabria/Sicily) and 1915 (Marsica) (6)
.
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ROOTS OF THE EPIDEMIOLOGICAL REVOLUTION
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Hippocrates, also known as the Father of Medicine, described 2400 years ago the influence of the environment on the human health. In fact, the man-environment binominal is also referred to as "Hippocrates’ dyad." During those times, the parallel roles of preventive medicine and curative medicine were already delineated. This is implicit in the first words of the well-known Hippocratic oath, enunciating a number of ethical principles of medical practice: "I swear by Apollo Physician and Asclepius and Hygeia and Panacea and all gods and goddesses..." In the Greek mythology, Hygeia and Panacea were daughters of Asclepius, the god of medicine. Of them, Panacea was the goddess who was worshipped by sick individuals with the hope to heal, while Hygeia was the goddess who was worshipped by healthy individuals with the hope to maintain their healthy status. Clearly, the word hygiene, the branch of medical sciences that relates to preservation of health, is etymologically derived from Hygeia.
After so many centuries, the decisive turning point occurred in the late 19th century with the discovery of bacteria and, later on, of other pathogens. These discoveries opened the way to targeted medical interventions aimed at preventing and curing infections and parasitic diseases. It was thus possible to control most communicable diseases in developed countries and, to an appreciable extent but with dramatic exceptions, in developing countries. Smallpox, a threat to humanity in the course of millennia, was eradicated worldwide 25 years ago, and other epidemiologically important infectious diseases are close to disappearing from the earth’s face.
Consequently, during the past 150 years infant mortality rate has been massively reduced, dropping in Italy from 220
in 1850 (more than 1 of 5 babies dying before becoming a year old!) to 167 in 1901 and 5 in 2000. In parallel, life expectancy at birth in Italy was almost doubled in the 20th century, being 44 years in 1901, a figure comparable to the levels of 35–40 years that had prevailed in Europe for centuries (2)
, and 79.6 years in 2000. Whereas in 1901 the gap between males and females was less than 1 year, in 2000 it was 6 years (76.6 in males and 82.6 in females). At the same time, as shown in Fig. 3
, the natality rate decreased during the 20th century from 33 to 9 live births, with an acceleration of this decline after the early 1960s. The mortality from all causes decreased from 22 to 9.7 (crude rates), with a cross between natality and mortality curves in 1993.
The fall in mortality for communicable diseases and the exceptional life prolongation explain why chronic diseases became the predominant cause of death during the 20th century. In fact, the incidence of this kind of diseases grows exponentially with age. For instance, in developed countries the ratio of death rates for vascular diseases, chronic respiratory diseases, and cancers of the digestive or respiratory tract is more than 1000 at age 80 as compared with age 20 (7)
. For this reason, the shape of mortality curves for specific diseases is well diversified when considering age-standardized data (Fig. 2)
rather than crude data (Fig. 1)
. The same is true for deaths from all causes (Fig. 3)
, as shown, for example, by the fact that in 2000 the age-adjusted mortality rate in males was about the half that of the corresponding crude mortality rate; in females it was as much as 3.4-fold lower. In contrast, at the beginning of the 20th century there was no remarkable difference. In addition, crude and age-adjusted rates were very similar in the two genders in 1901 but in 2000, unlike crude mortality, age-adjusted mortality was largely different by gender: 2.9 in females and 5 in males.
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A NEW EPIDEMIOLOGICAL TURNING POINT IN THE LATE 20TH CENTURY
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Thus, in the second half of the 20th century chronic degenerative diseases gained an outstanding impact in terms of mortality in the population in Italy and other European countries as well as other industrialized countries, such as the U.S. (8)
and Japan (9)
. In addition to their prominent mortality role, chronic diseases are characterized by very high yet hardly quantifiable morbidity rates and by a trend to an incomplete restitutio ad integrum, which often leads to relapses and invalidity. The problem with the control of chronic degenerative diseases is that they are not caused by specific etiological agents. Rather, there is an intricate network that connects multiple diseases with multiple risk factors and, luckily, with multiple protective factors. From the point of view of preventive medicine, this implies that avoidance of exposure to a single risk factor will have a more or less evident beneficial effect on the epidemiology of several diseases. On the other hand, this strategy will never succeed in a complete eradication, because each disease is in turn associated with other risk factors. Due to the huge number of clinical entities involved, no generalization can be made. Nevertheless, it is noteworthy that some chronic diseases share common risk factors and protective factors as well as common pathogenetic mechanisms, such as DNA damage, oxidative stress, and chronic inflammation (10)
. This circumstance may justify, in some cases, the implementation of similar prevention strategies, based on avoidance of exposure to recognized risk factors and on the intake of protective factors. In fact, it is possible to modulate the host defense machinery by pursuing a chemopreventive approach based on dietary and pharmacological means.
A new epidemiological turning point became apparent in the second half of the 20th century. The start of the mortality decline for chronic degenerative diseases, after a steep escalation lasting many decades, represents a milestone in the history of medicine. The drop of mortality for cardiovascular and cerebrovascular diseases is a reality in most countries in the world, which may be ascribed to a variety of factors, including 1) artifacts due to a more reliable diagnosis of causes of death in recent years, 2) improvements in therapy, both medical and surgical, 3) fulfillment of primary prevention aimed at improving lifestyle and environmental conditions, 4) implementation of secondary prevention measures, and 5) amelioration of tertiary prevention and rehabilitation. Although not as important as in other countries, such as in the U.S., where the mortality rates for heart diseases were indeed much higher than in Mediterranean countries during the past decades (11)
, in Italy this trend was well evident, as shown in Figs. 1
and 2
. By taking into account crude data (Fig. 1)
, in the 1976–2000 period the mortality for cardiovascular diseases in Italy decreased from 351.6 to 286.0 per 100,000 in males (–18.7%) and from 338.6 to 313.5 in females (–7.4%). Taking into account age-adjusted data (Fig. 2)
, the top level in males was 273.5 in 1963, then went down to 131.6 per 100,000 in 2000 (–51.9%). In females, there were not important variations from 1901 to 1956, when the age-adjusted rate was 233.5; it gradually decreased to 74.9 per 100,000 in 2000 (–67.9%). As for cerebrovascular diseases, the crude mortality rate (Fig. 1)
went down in males from a maximum of 150.1 in 1940 to 97.8 per 100,000 in 2000 (–34.8%) and in females from 151.6 in 1985 and 1986 to 134.7 in 2000 (–11.1%). The drop in age-adjusted mortality rates for cerebrovascular diseases began after the first half of the century: in males from 152.4 in 1928 to 42.0 per 100,000 in 2000 (–72.4%) and in females from 123.2 in 1940 to 31.5 in 2000 (–74.4%).
The decrease in mortality from cancer is more recent. For a few years, this trend could be explained in terms of varied age composition of the population (12)
. As can clearly be inferred from a comparison of Figs. 1
and 2
, in very recent years the slow decline of cancer deaths became detectable even by analyzing crude mortality data, at least in males. Taking into account age-adjusted data (Fig. 2)
, mortality for all tumors in Italy decreased in males from a maximum of 196.2 in 1987 to 160.2 per 100,000 (–18.3%) in 2000. In females, it reached a plateau of 100 per 100,000 in the period from 1956 to 1989, then decreased to 87.1 (–12.9%) in the 2000. The success of preventive medicine is attested to by the fact that, since the early 1990s in the U.S. there has been a decline not only in cancer mortality, partly attributable to improvements in diagnosis and therapy, but also in cancer incidence (13)
, which depends solely on the effectiveness of prevention. A similar trend occurred in the European Union, where in 1997 for the first time there was a decrease of mortality corresponding to the avoidance of 80,000 deaths due mainly to a decrease in deaths from cancers of the stomach (–30% in 1988–1997), lung (–10%), intestines (–15%), breast (–10%), uterus, mainly cervix (–22%), leukemias (–10%), and, after 1995, prostate cancer (–3%) (14)
. Indeed, together with the persisting downward trend of deaths from stomach cancer, attenuation of the dramatic epidemic of lung cancer in the male population, due to changes in smoking habits, is the leading factor in the overall decline in mortality from cancer in Italy (15)
and many other Western countries. Unfortunately, an opposite trend can easily be predicted for the next few decades in many developing countries (2)
.
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CONCLUSIONS
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The analysis reported here promises to be a basis for public health interventions in Italy and a model for similar analyses in developed and developing countries. Notwithstanding the enormous health and social problems that have always affected humankind, the data reported in the present article highlight the tremendous progress achieved at the end of the second millennium. The drop in general mortality in Italy (see Fig. 3
) gives a measure of this progress. In the year 1871, with a population of 26 million, the crude mortality rate was 30. In 1901, with a population of 33 million, the mortality rate was 22. In 2000, with a population of almost 58 million, the mortality rate was 9.7%. By hypothetically assuming that, with the present Italian population size, general mortality rates had remained those of 1871 or 1901, in 2000 there would have been 1,740,000 or 1,276,000 deaths, respectively, rather than 560,000 deaths. In other words, the breakthrough of preventive, curative, and rehabilitative medicine, along with the improvement of hygienic conditions, has been so spectacular that, in a country such as Italy, by the end of the 20th century as many as 1,180,000 or 716,000 lives a year were saved compared with 1871 or 1901.
Clearly, the progressive decrease of natality and general mortality, and the parallel aging of the population, underlie important social issues and solicit adequate rehabilitative and assistential programs in the elderly. The described epidemiological trends render even more meaningful the modern definition of health given in 1946 by WHO. The goal of reducing morbidity and mortality for diseases and infirmities, which has partially been achieved, must be complemented by promotion of physical, mental, and social well-being, which is an even more difficult challenge. In fact, nowadays a higher number of people survive longer but often suffer from various degrees of disability, which should be taken into due account by health care planners.
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ACKNOWLEDGMENTS
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We thank Anna Maria Grondona, Francesco Ricci, and Simone Manenti for their skilful assistance in collecting the data. Preparation of this article was supported by the Associazione Italiana per la Ricerca sul Cancro (AIRC).
Received for publication December 5, 2004.
Accepted for publication February 8, 2005.
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TOP
ABSTRACT
INTRODUCTION
