The History and Scope of Epidemiology
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• Define the term epidemiology
• Define the components of epidemiology (determinants, distribution, morbidity, and mortality)
• Name and describe characteristics of the epidemiologic approach
• Discuss the importance of Hippocrates’ hypothesis and how it differed from the common beliefs of the time
• Discuss Graunt’s contributions to biostatistics and how they affected modern epidemiology
• Explain what is meant by the term natural experiments, and give at least one example
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Infectious and Chronic Disease • Hepatitis A outbreak – Utah
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Utah Opioid Drug Deaths • In 2014, 32% of adults were prescribed an opiod pain
• 23 individuals die in Utah each month to overdose
– Outpaces deaths due to firearms, falls, and motor
– Utah ranks 7th in the U.S. for drug poisoning deaths
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Epidemiology is more than
infectious and chronic diseases
Epidemiology is more than
infectious and chronic diseases
• Epidemiology derives from “epidemic,”
originating from the Greek words
– epi – prefix meaning on, upon, or befall
– demos – root meaning the people
– logos – suffix meaning the study
• In other words, epidemiology is the study
of what befalls the population
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Definition of Epidemiology
• Epidemiology is concerned with the
distribution and determinants of health and
diseases, morbidity, injuries, disability, and
mortality in populations.
• Epidemiologic studies are applied to the
control of health problems in populations.
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• Factors or events that are capable of
bringing about a change in health.
• Search for causes and other factors of
health-related states or events.
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Examples of Determinants
• Health-related states or events
• Disease states
• Biologic agents – bacteria, virus, fungus
• Chemical agents – carcinogens
• Conditions associated with health
• Physical activity or high-fat diet
• Environmental poisoning
• Seat belt use
• Provision and use of health services
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The Search for Determinants
• Numerous examples in textbook
– 1970s Love Canal – Hooker chemical
and Niagara Fall, NY
– 1980 Red Spots on Eastern Airline
Flight Attendants–dye from life vests
– 1993 Hantavirus outbreak
• 4 corners (Utah)
– 2001 Anthrax outbreak
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Cases • Index case reported in
• Additional cases,
including fatal cases,
reported in New York,
New Jersey, Connecticut.
• Contaminated mail linked
to some of the cases.
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• Study of frequency and pattern of health
events in the population
• Frequency – number, and number in
relation to the population
• Pattern – the health-related state or event
by person, place, and time characteristics
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Disease Distribution Examples
• CHD death rates and stroke were higher
among African-Americans than among
American Indian/Alaskan natives,
Asian/Pacific Islanders, or whites – What are the underlying factors?
• HIV rates in Utah from 2000-2010 are 40
times higher in African-born immigrants
living in Utah than Utah Caucasian males – Even though there are more cases in Caucasian-males
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• Epidemiology examines disease
occurrence among population groups,
– TSS increase in the 1980’s
• Epidemiology is often referred to as
• The epidemiologic description indicates
variation by age groups, time,
geographic location, and other variables.
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• Epidemiology investigates many
different kinds of health outcomes:
– Infectious diseases
– Chronic diseases
– Disability, injury, limitation of activity
– Active life expectancy
– Mental illness, suicide, drug addiction
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Morbidity and Mortality
• Morbidity–designates illness.
• Mortality–refers to deaths that occur in a
population or other group.
• Note that most measures of morbidity and
mortality are defined for specific types of
morbidity or causes of death.
– What do we do with this data?
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Aims and Levels
• To describe the health status of
• To explain the etiology of disease.
• To predict the occurrence of disease.
• To control the occurrence of disease.
– Intervention or Prevention
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Epidemiology Is Interdisciplinary
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Foundations of Epidemiology • Interdisciplinary
– Infant botulism
• Methods and procedures
– Qualitative, demographic data – See next slide
• Use of special vocabulary
– Epidemic, pandemic, attack rate
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• Quantification is a central activity of
• Epidemiologic measures often require
counting the number of cases of disease.
• Disease distributions are examined
according to demographic variables such
as age, sex, and race.
– Also qualitative data
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Methods of quantification
• Leading cause of
• 1900 compared to
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Epidemic frequency of disease • What is an epidemic….endemic?
• How is this determined?
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1/9/2018 25 https://www.cdc.gov/flu/weekly/usmap.htm
– Current data
suggests that 2017-18
Infectious Disease Epidemics
• A single case of a long absent
• First invasion of a communicable
• Two cases of such a disease associated
in time and place are
sufficient evidence of
transmission to be
considered an epidemic. 1/9/2018 261: History & Scope
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Infectious disease triangle
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Pandemic • “ . . . an epidemic on a worldwide scale; during a pandemic, large
numbers of persons may be affected and a disease may cross
international borders.” An example is a flu pandemic.
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Concept of Epidemic and Non-
• Some examples that use the concept of an
– Love Canal
– Asbestosis among shipyard workers
– Diseases associated with lifestyle
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Ascertainment of Epidemics
– The systematic collection of data pertaining to
the occurrence of specific diseases.
– Analysis and interpretation of these data.
– Dissemination of disease-related information.
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Ascertainment of Epidemics
• Epidemic Threshold
– The minimum number of cases (or deaths)
that would support the conclusion that an
epidemic was underway.
• Are 10 obese individuals in this classroom
• Is one case of human anthrax infection an
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Historical Epidemiological Antecedents
• Environment and disease
• The Black Death
• Use of mortality counts
• Smallpox vaccination
• Use of natural experiments
• Identification of specific agents of disease
• The 1918 influenza pandemic
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• Hippocrates wrote On Airs, Waters, and
Places in 400 BC.
• Father of medicine and first epidemiologist
• He suggested that disease might be
associated with the physical environment. – Malaria and swampy water
• Represented a movement
away from supernatural
explanations of disease
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The Black Death • Occurred between 1346-1352
• Claimed one-quarter to one-third of
population of Europe
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Use of Mortality Counts
• John Graunt, in 1662, published Natural
and Political Observations Made upon the
Bills of Mortality. – Recorded how many persons per year died of what
kind of event or disease
– Developed and calculated life tables and life
– Divided deaths into two types of causes
• Acute (struck suddenly – e.g., cholera)
• Chronic (lasted over a long period of time – e.g.,
emphysema) 1/9/2018 391: History & Scope
• Jenner attempted to give a
dairymaid, exposed to a mild
case of cowpox in her youth, a
case of cowpox by cutting her
arm and rubbing some of the
infectious “grease” into the
wound. She did not get ill.
• He subsequently invented a
vaccination for smallpox
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Use of Natural Experiments
• John Snow was an
English physician and
• He investigated a
cholera outbreak that
occurred during the
mid-19th century in
Broad Street, Golden
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• Linked the cholera epidemic
to contaminated water
• Used a spot map of cases
and tabulation of fatal
attacks and deaths.
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Snow’s Natural Experiment
• Two different water companies supplied water from the Thames River to houses in the same area.
• The Lambeth Company moved its source of water to a less polluted portion of the river.
• Snow noted that during the next cholera outbreak those served by the Lambeth Company had fewer cases of cholera.
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• Black lines
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• Definition: The epidemiologist does not
manipulate a risk factor but rather
observes the changes in an outcome as
the result of a naturally occurring
• Contemporary Natural Experiments
– Currently, natural experiments may be the
result of legislation, policy changes or
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Examples of Contemporary
• Seat Belt Law–Did seat belt use reduce
fatalities from motor vehicle accidents?
• Tobacco Tax–Did the increase in cigarette
price decrease the sale of cigarettes?
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Ignaz Semmelweis • Mid 1800’s
• Described as the “savior of mothers”
• Early pioneer of antiseptic procedures
• Proved that childbed fever resulted from physicians not washing their hands after dissections
• Could not “prove” and many disregarded recommendation until Louis Pasteur and germ theory
• Appointed compiler of abstracts in
• Provided foundation for classification of
– International Classification of Disease system
• Examined linkage between mortality rates
and population density.
– Healthier population districts
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Koch’s Postulates • Robert Koch – Established germ theory
• Microorganism must be observed in every
case of the disease.
• Microorganism must be isolated and grown in
• Pure culture must, when inoculated into a
susceptible animal, reproduce the disease.
• Microorganism must be observed in, and
recovered from, diseased animal.
– Anthrax was transmissible
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The 1918 Influenza Pandemic • Occurred between 1918 and 1919
• Killed 50- to 100 million persons
• 2.5% case-fatality rate versus 0.1% for
other influenza pandemics
• Deaths most
20- to 40-year-olds
– How is that different
than today? 1/9/2018 511: History & Scope
Recent Applications of
• Framingham Heart Study (since 1948)
– Investigates coronary heart disease risk
• Smoking and lung cancer; e.g., Doll and
Peto’s study of British doctors’ smoking.
• AIDS, chemical spills, breast cancer
screening, secondhand smoke.
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Additional Applications of
Epidemiology • Infectious diseases
– Avian influenza, H1N1, Listeria
• Environmental health
• Chronic diseases
• Lifestyle and health promotion
• Psychiatric and social epidemiology
• Molecular and genetic epidemiology
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