Epidemiology Kept Simple Chapter 1 Epidemiology Past & Present



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Epidemiology Kept Simple

  • Chapter 1

  • Epidemiology Past & Present


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


§1.1 Epidemiology, Health, and Public Health

  • What is Epidemiology?

  • What is Public Health?

  • What is Health?



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)


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


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?



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


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



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

  • Historical study

  • Community diagnosis

  • Working of health services

  • Individual chances

  • Complete clinical picture

  • Identify new syndromes

  • Determine cause (ultimate importance)



§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



Leading Causes of Death



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. (don’t over-simplify!)


Demographic Transition



U. S. Mortality 1950 – 1990 Discuss (Fig 1.2, p. 8)



Mortality, Selected Cancer, U. S. (Fig. 1.3, p. 9)



Life Expectancy at Birth (Fig. 1.4, p. 10)



§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)


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


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



Demographic Approach

  • John Graunt (1620 – 1674)

  • pp. 12 – 14



Graunt’s Life Table % surviving to age



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



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)


John Snow

  • Quintessential epidemiologic hero

  • Physiologist, anesthesiologist, & epidemiologist

  • Remembered for

    • Insightful theory of disease
    • Impressive methods of studies


Snow’s 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


Components of Snow’s Contagion Theory

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


Snow’s Methods

  • Snow’s 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


Snow’s Ecological Study Figure 1.13 (p. 24)



Ecological Study Key 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


Snow’s 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



Snow’s 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



Snow’s 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}



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



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?



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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