The History and Scope of Epidemiology

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Chapter 1

• The History and Scope of Epidemiology

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Tap Water Increases Miscarriages

• Swan et al. (1998) released results on total
  trihalomethanes (TTHMs) in drinking water.
• Human exposure to TTHMs may be related to adverse
  pregnancy outcomes.

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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.

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Epidemiology Defined

• Epidemiology derives from "epidemic," a term
  which provides an immediate clue to its subject
  matter. Epidemiology originates from the Greek
  words, epi (upon) demos (people) logy (study
  of).

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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.

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Key Aspects of This Definition

• Determinants
• Distribution
• Population
• Health phenomena
• Morbidity and mortality

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Determinants

• Factors or events that are capable of bringing
  about a change in health.

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Examples of Determinants

• Biologic agents--bacteria
• Chemical agents--carcinogens
• Less specific factors--stress, drinking,
  sedentary lifestyle, or high-fat diet

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The Search for Determinants

• Outbreak of Fear--Ebola virus in Kikwit, Zaire
• Fear on Seventh Ave.--Legionnaires disease in
  New York City
• Red Spots on Airline Flight Attendants--dye from
  life vests

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Distribution

• Frequency of disease occurrence may vary from one
  population group to another.

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Disease Distribution Examples

• Hypertension more common among young black men
  than among young white men.
• Coronary heart disease occurrence differs between
  Hispanics and non-Hispanics.

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Population

• Epidemiology examines disease occurrence among
  population groups, not individuals.
• Epidemiology is often referred to as population
  medicine.
• The epidemiologic description indicates variation
  by age groups, time, geographic location, and
  other variables.

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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

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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.

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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.

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Foundations of Epidemiology

• Interdisciplinary
• Methods and procedures--quantification
• Use of special vocabulary
• Epidemic frequency of disease

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Epidemiology Is Interdisciplinary

• Epidemiology is an interdisciplinary field that
  draws from biostatistics and the social and
  behavioral sciences, as well as from the
  medically related fields of toxicology,
  pathology, virology, genetics, microbiology, and
  clinical medicine.

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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.

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Epidemic

• The occurrence in a community or region of cases
  of an illness (or an outbreak) clearly in excess
  of expectancy
• Relative to usual frequency of the disease.

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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.

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Concept of Epidemic and Non-infectious Diseases

• Some examples that use the concept of an epidemic
  are
• Love Canal
• Brown lung disease
• Asbestosis among shipyard workers
• Diseases associated with lifestyle

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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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Ascertainment of Epidemics

• Surveillance
• Epidemic threshold

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Surveillance

• 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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Epidemic Threshold

• The minimum number of cases (or deaths) that
  would support the conclusion than an epidemic was
  underway.

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Historical Antecedents

• Environment and disease
• Use of mortality counts
• Use of natural experiments
• Identification of specific agents of disease

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The Environment

• Hippocrates wrote On Airs, Waters, and Places in
  400 BC.
• He suggested that disease might be associated
  with the physical environment.
• This represented a movement away from
  supernatural explanations of disease causation.

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Use of Mortality Counts

• John Graunt, in 1662, published Natural and
  Political Observations Made upon the Bills of
  Mortality.

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John Graunts Contributions

• Recorded seasonal variations in births and
  deaths.
• Showed excess male over female differences in
  mortality.
• Known as the Columbus of biostatistics.

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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.

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Snows Contributions

• Linked the cholera epidemic to contaminated water
  supplies.
• Used a spot map of cases and tabulation of fatal
  attacks and deaths.

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Snows 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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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.

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Contemporary Natural Experiments

• Currently, natural experiments may be the result
  of legislation, policy changes or environmental
  interventions.

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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?
• Helmet Law--Did requiring the use of helmets by
  motorcyclists reduce the number of head injuries
  sustained?

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William Farr

• Appointed compiler of abstracts in England, 1839.
• Provided foundation for classification of
  diseases (ICD system).
• Examined linkage between mortality rates and
  population density.

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Koch's Postulates

• 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.

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Other Historical Developments

• Alexander Langmuir established CDCs
  Epidemiologic Intelligence Service.
• Wade Hampton Frost was the first professor of
  epidemiology in the U.S.
• Joseph Goldberger discovered the cure for
  pellagra.

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Recent Applications of Epidemiology

• Framingham Heart Study (since 1949) investigates
  coronary heart disease risk factors.
• Smoking and lung cancer e.g., Doll and Petos
  study of British doctors smoking.
• AIDS, chemical spills, breast cancer screening,
  secondhand smoke.

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Additional Applications of Epidemiology

• Infectious diseases
• Environmental health
• Chronic diseases
• Lifestyle and health promotion
• Psychiatric and social epidemiology
• Molecular and genetic epidemiology