The History and Scope of Epidemiology
The History and Scope of Epidemiology
Epidemiology PubH4040
1/9/2018 11: History & Scope
Learning Objectives
• 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
1/9/2018 21: History & Scope
Infectious and Chronic Disease • Hepatitis A outbreak – Utah
– https://www.ksl.com/?sid=46232231&nid=148
• –
1/9/2018 1: History & Scope 3
Utah Opioid Drug Deaths • In 2014, 32% of adults were prescribed an opiod pain
reliever
• 23 individuals die in Utah each month to overdose
– Outpaces deaths due to firearms, falls, and motor
vehicles
– Utah ranks 7th in the U.S. for drug poisoning deaths
1/9/2018 1: History & Scope 4
Epidemiology is more than
infectious and chronic diseases
Epidemiology is more than
infectious and chronic diseases
Epidemiology Defined
• 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
1/9/2018 71: History & Scope
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.
1/9/2018 81: History & Scope
Determinants
• 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.
1/9/2018 91: History & Scope
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
• Nutrition
• Environmental poisoning
• Seat belt use
• Provision and use of health services
1/9/2018 101: History & Scope
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
• Bioterrorism
1/9/2018 111: History & Scope
Bioterrorism-Associated Anthrax
Cases • Index case reported in
Florida.
• Additional cases,
including fatal cases,
reported in New York,
New Jersey, Connecticut.
• Contaminated mail linked
to some of the cases.
1/9/2018 121: History & Scope
Distribution
• 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
1/9/2018 131: History & Scope
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
1/9/2018 141: History & Scope
Population
• Epidemiology examines disease
occurrence among population groups,
not individuals.
– TSS increase in the 1980’s
• Epidemiology is often referred to as
population medicine.
• The epidemiologic description indicates
variation by age groups, time,
geographic location, and other variables.
1/9/2018 151: History & Scope
Health Phenomena
• Epidemiology investigates many
different kinds of health outcomes:
– Infectious diseases
– Chronic diseases
– Disability, injury, limitation of activity
– Mortality
– Active life expectancy
– Mental illness, suicide, drug addiction
1/9/2018 161: History & Scope
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?
1/9/2018 171: History & Scope
Aims and Levels
• To describe the health status of
populations.
• To explain the etiology of disease.
• To predict the occurrence of disease.
• To control the occurrence of disease.
– Intervention or Prevention
1/9/2018 181: History & Scope
Epidemiology Is Interdisciplinary
1/9/2018 191: History & Scope
Foundations of Epidemiology • Interdisciplinary
– Infant botulism
• Methods and procedures
– Quantification
– Qualitative, demographic data – See next slide
• Use of special vocabulary
– Epidemic, pandemic, attack rate
1/9/2018 201: History & Scope
Quantification
• Quantification is a central activity of
epidemiology.
• 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
1/9/2018 211: History & Scope
Methods of quantification
• Leading cause of
mortality
• 1900 compared to
2009
1/9/2018 1: History & Scope 22
1/9/2018 1: History & Scope 23
Epidemic frequency of disease • What is an epidemic….endemic?
• How is this determined?
1/9/2018 1: History & Scope 24
1/9/2018 25 https://www.cdc.gov/flu/weekly/usmap.htm
– Current data
suggests that 2017-18
vaccine is
approximately 39%
effective
Infectious Disease Epidemics
• A single case of a long absent
communicable disease.
• First invasion of a communicable
disease.
• 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
1/9/2018 1: History & Scope 27
Infectious disease triangle
1/9/2018 1: History & Scope 28
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.
291: History & Scope
Concept of Epidemic and Non-
Infectious Diseases
• Some examples that use the concept of an
epidemic are:
– Love Canal
– Asbestosis among shipyard workers
– Diseases associated with lifestyle
1/9/2018 301: History & Scope
Ascertainment of Epidemics
• Surveillance
– The systematic collection of data pertaining to
the occurrence of specific diseases.
– Analysis and interpretation of these data.
– Dissemination of disease-related information.
1/9/2018 311: History & Scope
1/9/2018 1: History & Scope 32
1/9/2018 1: History & Scope 33
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
an epidemic?
• Is one case of human anthrax infection an
epidemic?
1/9/2018 341: History & Scope
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
1/9/2018 351: History & Scope
The Environment
• 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
causation.
1/9/2018 361: History & Scope
The Black Death • Occurred between 1346-1352
• Claimed one-quarter to one-third of
population of Europe
1/9/2018 371: History & Scope
1/9/2018 1: History & Scope 38
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
expectancy
– 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
Edward Jenner
• 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
1/9/2018 401: History & Scope
Use of Natural Experiments
• John Snow was an
English physician and
anesthesiologist.
• He investigated a
cholera outbreak that
occurred during the
mid-19th century in
Broad Street, Golden
Square, London.
1/9/2018 411: History & Scope
Snow’s Contributions
• Linked the cholera epidemic
to contaminated water
supplies.
• Used a spot map of cases
and tabulation of fatal
attacks and deaths.
1/9/2018 421: History & Scope
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.
1/9/2018 431: History & Scope
• Black lines
represent case
of cholera
1/9/2018 44
1/9/2018 1: History & Scope 45
Natural Experiment
• Definition: The epidemiologist does not
manipulate a risk factor but rather
observes the changes in an outcome as
the result of a naturally occurring
situation.
• Contemporary Natural Experiments
– Currently, natural experiments may be the
result of legislation, policy changes or
environmental interventions.
1/9/2018 461: History & Scope
Examples of Contemporary
Natural Experiments
• 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?
1/9/2018 471: History & Scope
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
William Farr
• Appointed compiler of abstracts in
England, 1839.
• Provided foundation for classification of
diseases
– International Classification of Disease system
• Examined linkage between mortality rates
and population density.
– Healthier population districts
1/9/2018 491: History & Scope
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.
• 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
1/9/2018 501: History & Scope
The 1918 Influenza Pandemic • Occurred between 1918 and 1919
• Killed 50- to 100 million persons
worldwide
• 2.5% case-fatality rate versus 0.1% for
other influenza pandemics
• Deaths most
frequent among
20- to 40-year-olds
– How is that different
than today? 1/9/2018 511: History & Scope
Recent Applications of
Epidemiology
• Framingham Heart Study (since 1948)
– Investigates coronary heart disease risk
factors.
• Smoking and lung cancer; e.g., Doll and
Peto’s study of British doctors’ smoking.
• AIDS, chemical spills, breast cancer
screening, secondhand smoke.
1/9/2018 521: History & Scope
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
1/9/2018 531: History & Scope