Epidemiology Kept Simple

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Epidemiology Kept Simple

• Chapter 1
• Epidemiology Past Present

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Comments re Text

• EKS Epidemiology Kept Simple
• 20 chapters
• We cover about 8
• Multiple sections () per chapter
• We do not cover all sections in chapters
• Chapter outline on first page
• To help organize thinking

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1.1 Epidemiology, Health, and Public Health

• What is Epidemiology?
• What is Public Health?
• What is Health?

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Epidemiology Defined

• Greek roots
• epi upon
• demos the people
• ology study of
• Literally - study of epidemics
• Modern definitions include references to
• distributions of health determinant (statistical
  concept)
• determinants of disease (pathophysiologic
  concept)
• application in control of health problems
  (biological and social concepts)

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Comparison of epi annd medicine

• Main unit of concern
• Epi - population
• Medicine -- individual
• But
• Epi becoming more medical over time
• Medicine becoming more epidemiologic over time

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Public Health

• Definitions include reference to
• organized effort (activity)
• reduction of morbidity / mortality and improved
  health
• Composed of dozens of disciplines
• e.g., microbiology, psychology, administration,
  epidemiology, health ed., etc.
• Has been called undisciplined
• Comparison of epi and public health
• epi a study of
• pub health an activity
• Follow-up on WebCT discussion board?

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Health

• Multiple definitions (cultural specific?)
• WHO (1948) defined health as well-being
• Not merely the absence of disease
• Physical, mental, and social well-being
• Should definitions of health reference quality of
  life?
• Pros
• Cons

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Additional Terms

• Morbidity disease or disability
• Mortality death
• Occurrence of disease prevalence or incidence
  (will distinguish later in course)
• Endemic normal occurrence
• Epidemic greater than normal occurrence
• Pandemic epidemic on multiple continents

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1.2 Uses of Epi (Morris, 1957)see pp. 3 - 4

1. Historical study
2. Community diagnosis
3. Working of health services
4. Individual chances
5. Complete clinical picture
6. Identify new syndromes
7. Determine cause (ultimate importance)

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1.3 Epidemiologic Transition(pp. 4 10)

• This section of the text has section headings
• 20th century changes in disease patterns
• Mortality trends since 1950
• Life expectancy
• Intends to provide additional context

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Leading Causes of Death
1900 1990
1 Pneumonia / influenza Heart disease
2 TB Neoplasms
3 Diarrhea Cerbrovascular
4 Heart disease COPD
5 Cerebrovascular Pneumonia/ influenza
Large had infectious component
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Changes in mortality

• Epi transition
• Acute to chronic cause
• Infectious to life style cause
• Decrease mortality overall
• Death burden shifted to older ages
• Many causes
• Medical technology (antibiotics, anesthesia)
• Birth control
• Nutrition
• Sanitation and vector control
• Education
• Improved standard of living
• etc. (dont over-simplify!)

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Demographic Transition
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U. S. Mortality 1950 1990Discuss (Fig 1.2, p.
8)
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Mortality, Selected Cancer, U. S. (Fig. 1.3, p.
9)
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Life Expectancy at Birth (Fig. 1.4, p. 10)
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1.4 Selected Historical Figures and Events

• An essential part of the outfit of the
  investigator in the field (Major Greenwood)
• Headings in this section
• Before epi was a separate discipline
• Emergence of epi in Victorian England
• Twentieth century epi
• Smallpox (optional)

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Before Epi was a Discipline pp. 11 12

• We must understand the role of culture and
  western civilization
• Selected points
• Pre-scientific medicine was based on philosophy,
  religion, and morality
• Hippocrates symbolizes the shift to observation
  and the environment
• The Dark Ages represent a decline in
  enlightenment and public health
• The Protestant reformation brought with it
  important cultural changes

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Western Civilization and Scientific Revolution
(cont.)

• The renaissance brought with it an Age of
  Enlightenment
• Science liberates itself from philosophy,
  morality, and religion
• Post-modernism risks decadence

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Demographic Approach

• John Graunt (1620 1674)
• pp. 12 14

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Graunts Life Table surviving to age
6 64
16 40
26 25
36 16
46 10
56 6
60 3
76 1
80 0
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Lessons Learned from Graunt (Rothman, 1996)

• he was brief
• made reasoning clear
• subjected theories to multiple and varied tests
• invited criticism
• was willing to change ideas when confronted with
  contradictory evidence
• avoided mechanical interpretations

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Germ Theory(p. 14)

• Highlights
• Self-replicating (i.e., biological) agent
• Theory not accepted until late 1800s
• Competing theory (miasma atmospheric
  pollution) was accepted as late 1880s
• Early contagionists
• Fracastoro (first cogent germ theory, 16th
  century)
• Jakob Henle Robert Koch
• Pasteur
• Snow (see next section)
• Salmon (vector borne transmission)

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John Snow

• Quintessential epidemiologic hero
• Physiologist, anesthesiologist, epidemiologist
• Remembered for
• Insightful theory of disease
• Impressive methods of studies

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Snows Waterborne Theory

• Refuted miasma in favor of contagion
• Theory on
• Clinical facts symptoms and treatment
• Physiologic understanding death due to fluid
  loss, smudging of blood, and asphyxiation
• Epidemiologic observations epidemics followed
  routes of commerce, environmental contamination
  during epidemics

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Components of Snows Contagion Theory

• Free-living agent
• Fecal-oral transmission (person-to-person)
• Agent multiplies within the host
• Water-borne transmission

to age 16
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Snows Methods

• Snows methods are a model for non-experimental
  epi
• Three types of studies
• Ecological design compared cholera rates by
  region
• Cohort design compared cholera rates in exposed
  and non-exposed individuals
• Case-control design compared exposure status in
  those with and without disease

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Snows Ecological StudyFigure 1.13 (p. 24)
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Ecological StudyKey data in Figure 1.13 (p. 24)

• Example of rate calculation
• Rate St. Saviour 45 / 19,709 100,000 227
• Rate Christchurch 7 / 16,022 100,000 43
• Water source
• St. Saviour Southwark and Vauxhall Water Only
• Christchurch multiple water companies
  including Vauxhall

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Snows Cohort Study Key data in Table 1.7 (p. 25)

• Data by household
• Household water sources known
• Rates per 10,000 households cases / households
  10,000
• Main comparison
• Rate Southwark Vauxhall 1263 / 40,046
  10,000 315
• Rate Lambeth 98 / 26107 10,000 37.5
• Conclude Southwark Vauxhall households had 8.5
  time risk of Lambeth

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Snows Case-Control Study

• Collect data on all cases
• Determine source of water for cases and non-cases
  
• See pp. 23 26 for examples of interviews

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Snows Map of Golden Square Cholera Outbreak (Fig
1.14)

• Cases more likely to live near Broad St. pump
• Exceptions no cases in Brewery and few cases in
  Workhouse
• Paste section of map here

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Exposure to Broad St. Pump Water

• Case-control studies measure frequency of
  exposure (not frequency of disease)
• Consumption (exposure) frequent in cases
• 61 cases exposure confirmed
• 6 cases non-exposed
• 6 cases equivocal
• Exposure rare in non-cases
• Exposure more frequent in cases than controls

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Removal of Broad Street Pump Handle

• Snow supported his good theory with high
  quality data
• But how did he convince the Guardians of the
  Golden Square area to remove the pump handle?

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20th Century Epidemiology(p. 26)

• Addressing the chronic disease associated with
  epidemiologic Transition
• Illustrative examples
• British Doctors Study (Doll Hills studies of
  the effects of smoking)
• Framingham Heart Study (risk factors for heart
  disease, many investigators)