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Epidemiology Kept Simple

Epidemiology Kept Simple. Chapter 1 Epidemiology Past & Present. Epidemiology Defined. Greek roots epi = upon (as in “epidermis”) demos = the people (as in “democracy”) ology = “to speak of”, “to study” Modern definitions of epidemiology refer to Distributions of

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Epidemiology Kept Simple

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  1. Epidemiology Kept Simple Chapter 1 Epidemiology Past & Present Chapter 1

  2. Epidemiology Defined • Greek roots epi = upon (as in “epidermis”) demos = the people (as in “democracy”) ology = “to speak of”, “to study” • Modern definitions of epidemiology refer to • Distributions of • Health determinants • Disease and other health-related outcomes • Populations • Application in control of health problems Chapter 1

  3. Public Health Defined • Definition of public health • organized effort • Intended to reduce of morbidity & mortality and improve health • Core disciplines public health (CEPH / ASPH) • Epidemiology • Biostatistics • Health administration • Behavioral sciences • Environmental health sciences Chapter 1

  4. Epi compared to public health • Epidemiology  “study of” • Public health  “organized effort” • Epi = the “methodological backbone” of public health Chapter 1

  5. Basic Terms • Morbidity = related to disease or disability • Mortality = related to death • Endemic = normal occurrence of a condition • Epidemic = much greater than normal occurrence of a condition • Pandemic = an epidemic on multiple continents • Incidence = rate or risk of developing a condition • Prevalence = proportion of population with a condition Chapter 1

  6. Uses of Epi (Morris 1957) • Historical study • Community diagnosis • Working of health services • Individual chances • Completing the clinical picture • Identify new syndromes • Search for causes (paramount for prevention) Chapter 1

  7. Demographic Transition ↓ mortality ↓ fertility ↑ aging  change in shape of pop’n pyramid Chapter 1

  8. Epidemiologic Transition shift from acute contagious diseases to chronic lifestyle diseases Chapter 1

  9. Reasons for Epi.Transition During the first half of 20th century: • Improved standard of living • Vaccination • Improved nutrition • Sanitation and vector control During the second half of 20th century • Birth control • Improvements in lifestyle • Medical technology (e.g., antibiotics, treatment of hypertension, improved anesthetic safety) Chapter 1

  10. Causes of Death, U.S., 1950–1990 Chapter 1

  11. Mortality Trends of Selected Cancers U.S., 1940 - 1995 • Respiratory and prostate increased • Colorectal & stomach declined • Breast cancer about the same Chapter 1

  12. Life Expectancy Trends Dramatic increases all groups Rank White women Black women White males Black men Chapter 1

  13. Selected Historical Figures & Events • Hippocrates (400BCE) • Age of scientific enlightenment (17th & 18th centuries) • John Graunt (1620 – 1674) • Pierre Charles Louis (1787 – 1872) • John Snow (1813 – 1858) • Germ Theory (mid 19th century) • Modern epidemiology (post WWII) Chapter 1

  14. Enlightenment The birth of modern medicine and public health must be studied in the context of the Western Enlightenment (pp. 11–12). Barzun, J. (2001). From Dawn to Decadence: 500 Years of Western Cultural Life: New York: HarperCollins. Chapter 1

  15. Demographic Approach John Graunt (1620–74) Chapter 1

  16. Lesson from Graunt(Rothman, 1996) • Was brief • Made reasoning clear • Subjected theories to multiple and varied tests • Invited criticism • Willing to change ideas when confronted with contradictory evidence • Avoided simplistic interpretations of data Chapter 1

  17. Germ Theory (Highlights) • Until the 19th century, germ theory played second fiddle to vague theories of pollution (e.g., miasma theory) • Examples of early contagionists • Fracastoro (16th century Italian) • Henle & Koch (German physiologists) • John Snow (epidemiologist’s hero) • Pasteur (1865 experimental proof in silkworms) • Daniel Salmon (vector borne transmission) Chapter 1

  18. John Snow, Our Hero Snow’s cholera theory: • Epidemics follow routes of commerce • Agent is free-living & multiplies within the host • Transmission is water-borne, spread via fecal contamination, ingested orally • Patho-physiology: diarrhea  fluid loss  smudging of blood  asphyxiation  death John Snow (1813–1858) Chapter 1

  19. Snow’s Methods • Ecological comparisons: compared cholera rates by region • Cohort comparisons: compared cholera rates in exposed and non-exposed households • Case-control comparisons: compared exposure to contaminated water in cases and non-cases Chapter 1

  20. Ecological Comparisons • Southwark Water Company  high neighborhoods rates • Mixed service  intermediate rates • Lambeth Water Co. neighborhoods  no cases Chapter 1

  21. Cohort Comparisons Example of calculation: Southwark rate = 1263 / 40,046 = .0315 = 315 / 10,000 Chapter 1

  22. Snow’s mapquasicase-control Chapter 1

  23. Snow’s Quasi Case-Control Analysis • Cases more likely to be exposed to Broad St. pump water than non-cases (“controls”) • Among cases: • 61 used Broad St. water, 6 did not, and 6 were uncertain • Among controls: Broad St. water use was rare • e.g., at the Brewery (no cases) “the men …were allowed a certain quantity of malt liquor, and … do not drink water at all” Chapter 1

  24. Post-WWII (Modern) Epidemiology • Epidemiologic transition  shift in focus from acute infectious diseases to chronic life style diseases • Exemplar studies • The British Doctors Study • The Framingham Heart Study Chapter 1

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