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Epidemiology Kept Simple

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Title: Epidemiology Kept Simple


1
Epidemiology Kept Simple
  • Chapter 1
  • Epidemiology Past Present

2
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

3
1.1 Epidemiology, Health, and Public Health
  • What is Epidemiology?
  • What is Public Health?
  • What is Health?

4
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)

5
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

6
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?

7
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

8
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

9
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)

10
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

11
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
12
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!)

13
Demographic Transition
14
U. S. Mortality 1950 1990Discuss (Fig 1.2, p.
8)
15
Mortality, Selected Cancer, U. S. (Fig. 1.3, p.
9)
16
Life Expectancy at Birth (Fig. 1.4, p. 10)
17
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)

18
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

19
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

20
Demographic Approach
  • John Graunt (1620 1674)
  • pp. 12 14

21
Graunts Life Table surviving to age
6 64
16 40
26 25
36 16
46 10
56 6
60 3
76 1
80 0
22
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

23
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)

24
John Snow
  • Quintessential epidemiologic hero
  • Physiologist, anesthesiologist, epidemiologist
  • Remembered for
  • Insightful theory of disease
  • Impressive methods of studies

25
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

26
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
27
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

28
Snows Ecological StudyFigure 1.13 (p. 24)
29
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

30
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

31
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

32
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

33
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

34
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?

35
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)
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