Epidemiology Epidemiology Kept SimpleKept Simple

Chapter 1Chapter 1Epidemiology Past & PresentEpidemiology Past & Present

Comments re: Text Comments re: Text

• EKS = EKS = Epidemiology Kept SimpleEpidemiology Kept Simple • 20 chapters 20 chapters

• We cover about 8We cover about 8

• Multiple sections Multiple sections (§) per chapter(§) per chapter• We do We do not not cover all sections in chapterscover all sections in chapters

• Chapter outline Chapter outline on first pageon first page• To help organize thinkingTo help organize thinking

§1.1 Epidemiology, §1.1 Epidemiology, Health, and Public Health, and Public

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

Epidemiology DefinedEpidemiology Defined

• Greek rootsGreek roots• epi = uponepi = upon• demos = the peopledemos = the people• ology = study of ology = study of

• Literally - “study of epidemics”Literally - “study of epidemics”• Modern definitions include references to Modern definitions include references to

• distributions of health determinant (statistical distributions of health determinant (statistical concept)concept)

• determinants of disease (pathophysiologic concept)determinants of disease (pathophysiologic concept)• application in control of health problems application in control of health problems

(biological and social concepts)(biological and social concepts)

Comparison of epi annd Comparison of epi annd medicinemedicine

• Main unit of concernMain unit of concern• Epi –- populationEpi –- population• Medicine -- individualMedicine -- individual

• But … But … • Epi becoming more medical over timeEpi becoming more medical over time• Medicine becoming more Medicine becoming more

epidemiologic over timeepidemiologic over time

Public HealthPublic Health• Definitions include reference to Definitions include reference to

• organized effort (“activity”)organized effort (“activity”)• reduction of morbidity / mortality and improved reduction of morbidity / mortality and improved

healthhealth• Composed of dozens of disciplinesComposed of dozens of disciplines

• e.g., microbiology, psychology, administration, e.g., microbiology, psychology, administration, epidemiology, health ed., etc. epidemiology, health ed., etc.

• Has been called “undisciplined” Has been called “undisciplined” • Comparison of epi and public healthComparison of epi and public health

• epi = “a study of”epi = “a study of”• pub health = “an activity”pub health = “an activity”

• Follow-up on WebCT discussion board?Follow-up on WebCT discussion board?

HealthHealth

• Multiple definitions (cultural specific?)Multiple definitions (cultural specific?)• WHO (1948) defined health as “well-WHO (1948) defined health as “well-

being” being” • Not merely the absence of diseaseNot merely the absence of disease• Physical, mental, and social well-beingPhysical, mental, and social well-being

• Should definitions of health reference Should definitions of health reference quality of life?quality of life?• ProsPros• ConsCons

Additional TermsAdditional Terms

• Morbidity = disease or disabilityMorbidity = disease or disability• Mortality = death Mortality = death • Occurrence of disease = prevalence or Occurrence of disease = prevalence or

incidence (will distinguish later in course)incidence (will distinguish later in course)• Endemic = normal occurrenceEndemic = normal occurrence• Epidemic = greater than normal Epidemic = greater than normal

occurrenceoccurrence• Pandemic = epidemic on multiple Pandemic = epidemic on multiple

continentscontinents

§1.2 Uses of Epi (Morris, §1.2 Uses of Epi (Morris, 1957)1957)

see pp. 3 - 4see pp. 3 - 41.1. Historical studyHistorical study

2.2. Community diagnosisCommunity diagnosis

3.3. Working of health servicesWorking of health services

4.4. Individual chancesIndividual chances

5.5. Complete clinical pictureComplete clinical picture

6.6. Identify new syndromesIdentify new syndromes

7.7. Determine cause (ultimate Determine cause (ultimate importance)importance)

§1.3 §1.3 Epidemiologic Epidemiologic TransitionTransition

(pp. 4 – 10)(pp. 4 – 10)• This section of the text has section This section of the text has section

headings:headings:• 2020thth century changes in disease century changes in disease

patternspatterns• Mortality trends since 1950 Mortality trends since 1950 • Life expectancyLife expectancy

• Intends to provide additional Intends to provide additional contextcontext

Leading Causes of Leading Causes of Death Death

19001900 1990199011 Pneumonia / influenzaPneumonia / influenza Heart diseaseHeart disease

22 TBTB NeoplasmsNeoplasms

33 DiarrheaDiarrhea CerbrovascularCerbrovascular

44 Heart disease* Heart disease* COPDCOPD

55 Cerebrovascular*Cerebrovascular* Pneumonia/ influenzaPneumonia/ influenza

* Large % had infectious component

Changes in mortalityChanges in mortality• Epi transitionEpi transition

• Acute to chronic causeAcute to chronic cause• Infectious to “life style” causeInfectious to “life style” cause• Decrease mortality overall Decrease mortality overall • Death burden shifted to older agesDeath burden shifted to older ages

• Many causes Many causes • Medical technology (antibiotics, anesthesia)Medical technology (antibiotics, anesthesia)• Birth controlBirth control• NutritionNutrition• Sanitation and vector controlSanitation and vector control• Education Education • Improved standard of livingImproved standard of living• etc. (don’t over-simplify!)etc. (don’t over-simplify!)

Demographic Demographic TransitionTransition

U. S. Mortality 1950 – U. S. Mortality 1950 – 19901990

Discuss (Fig 1.2, p. 8)Discuss (Fig 1.2, p. 8)

Mortality, Selected Cancer, U. S. Mortality, Selected Cancer, U. S.

(Fig. 1.3, p. 9)(Fig. 1.3, p. 9)

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

§1.4 Selected Historical §1.4 Selected Historical Figures and EventsFigures and Events

• ““An essential part of the outfit of An essential part of the outfit of the investigator in the field” (Major the investigator in the field” (Major Greenwood)Greenwood)

• Headings in this sectionHeadings in this section• Before epi was a separate disciplineBefore epi was a separate discipline• Emergence of epi in Victorian EnglandEmergence of epi in Victorian England• Twentieth century epiTwentieth century epi• Smallpox (optional)Smallpox (optional)

Before Epi was a Before Epi was a DisciplineDiscipline pp. 11 – 12 pp. 11 – 12

• We must understand the role of culture We must understand the role of culture and western civilizationand western civilization

• Selected points:Selected points:• Pre-scientific medicine was based on Pre-scientific medicine was based on

philosophy, religion, and moralityphilosophy, religion, and morality• Hippocrates symbolizes the shift to Hippocrates symbolizes the shift to

observation and the environmentobservation and the environment• The Dark Ages represent a decline in The Dark Ages represent a decline in

enlightenment and public healthenlightenment and public health• The Protestant reformation brought with it The Protestant reformation brought with it

important cultural changesimportant cultural changes

                

Western Civilization Western Civilization and Scientific and Scientific

Revolution (cont.)Revolution (cont.)• The renaissance brought with it an The renaissance brought with it an

Age of Enlightenment Age of Enlightenment • Science liberates itself from Science liberates itself from

philosophy, morality, and religionphilosophy, morality, and religion• Post-modernism risks decadencePost-modernism risks decadence

Demographic ApproachDemographic Approach

• John Graunt (1620 – 1674)John Graunt (1620 – 1674)• pp. 12 – 14pp. 12 – 14

Graunt’s Life TableGraunt’s Life Table% surviving to age% surviving to age

66 6464

1616 4040

2626 2525

3636 1616

4646 1010

5656 66

6060 33

7676 11

8080 00

Lessons Learned from Graunt Lessons Learned from Graunt (Rothman, 1996)(Rothman, 1996)

• he was briefhe was brief• made reasoning clearmade reasoning clear• subjected theories to multiple and subjected theories to multiple and

varied testsvaried tests• invited criticisminvited criticism• was willing to change ideas when was willing to change ideas when

confronted with contradictory confronted with contradictory evidenceevidence

• avoided mechanical interpretationsavoided mechanical interpretations

Germ TheoryGerm Theory(p. 14)(p. 14)

• HighlightsHighlights• Self-replicating (i.e., biological) agent Self-replicating (i.e., biological) agent

• Theory not accepted until late 1800sTheory not accepted until late 1800s• Competing theory (“miasma” = atmospheric Competing theory (“miasma” = atmospheric

pollution) was accepted as late 1880spollution) was accepted as late 1880s

• Early contagionists Early contagionists • Fracastoro (first cogent germ theory, 16Fracastoro (first cogent germ theory, 16thth century) century)• Jakob Henle & Robert Koch Jakob Henle & Robert Koch • Pasteur Pasteur • Snow (see next section)Snow (see next section)• Salmon (vector borne transmission)Salmon (vector borne transmission)

John SnowJohn Snow

• Quintessential epidemiologic heroQuintessential epidemiologic hero• Physiologist, anesthesiologist, & Physiologist, anesthesiologist, &

epidemiologistepidemiologist• Remembered for Remembered for

• Insightful theory of diseaseInsightful theory of disease• Impressive methods of studiesImpressive methods of studies

Snow’s Waterborne Snow’s Waterborne TheoryTheory

• Refuted miasma in favor of contagion Refuted miasma in favor of contagion • Theory on Theory on

• Clinical facts: symptoms and treatmentClinical facts: symptoms and treatment• Physiologic understanding: death due to Physiologic understanding: death due to

fluid loss, smudging of blood, and fluid loss, smudging of blood, and asphyxiationasphyxiation

• Epidemiologic observations: epidemics Epidemiologic observations: epidemics followed routes of commerce, followed routes of commerce, environmental contamination during environmental contamination during epidemicsepidemics

Components of Snow’s Components of Snow’s Contagion TheoryContagion Theory

• Free-living agentFree-living agent• Fecal-oral transmission (person-to-Fecal-oral transmission (person-to-

person)person)• Agent multiplies within the hostAgent multiplies within the host• Water-borne transmissionWater-borne transmission

to age 16to age 16

Snow’s MethodsSnow’s Methods

• Snow’s methods are a model for Snow’s methods are a model for non-experimental epinon-experimental epi

• Three types of studiesThree types of studies• Ecological design: compared cholera Ecological design: compared cholera

rates by regionrates by region• Cohort design: compared cholera rates Cohort design: compared cholera rates

in exposed and non-exposed individualsin exposed and non-exposed individuals• Case-control design: compared Case-control design: compared

exposure status in those with and exposure status in those with and without diseasewithout disease

Snow’s Ecological Snow’s Ecological StudyStudy

Figure 1.13 (p. 24)Figure 1.13 (p. 24)

Ecological StudyEcological StudyKey data in Figure 1.13 (p. 24)Key data in Figure 1.13 (p. 24)

• Example of rate calculationExample of rate calculation• Rate Rate St. SaviourSt. Saviour = 45 / 19,709 × 100,000 = 227 = 45 / 19,709 × 100,000 = 227

• Rate Rate ChristchurchChristchurch = 7 / 16,022 × 100,000 = 43 = 7 / 16,022 × 100,000 = 43

• Water sourceWater source• St. Saviour – Southwark and Vauxhall Water St. Saviour – Southwark and Vauxhall Water

OnlyOnly• Christchurch – multiple water companies Christchurch – multiple water companies

including Vauxhallincluding Vauxhall

Snow’s Cohort Study Snow’s Cohort Study Key data in Table 1.7 (p. 25)Key data in Table 1.7 (p. 25)

• Data by household Data by household • Household water sources known Household water sources known • Rates per 10,000 households = cases / Rates per 10,000 households = cases /

households × 10,000households × 10,000• Main comparison:Main comparison:

• Rate Rate Southwark & VauxhallSouthwark & Vauxhall = 1263 / 40,046 × 10,000 = = 1263 / 40,046 × 10,000 = 315315

• Rate Rate LambethLambeth = 98 / 26107 × 10,000 = 37.5 = 98 / 26107 × 10,000 = 37.5• Conclude: Southwark & Vauxhall Conclude: Southwark & Vauxhall

households had 8.5 time risk of Lambethhouseholds had 8.5 time risk of Lambeth

Snow’s Case-Control Snow’s Case-Control StudyStudy

• Collect data on all casesCollect data on all cases• Determine source of water for Determine source of water for

cases and non-cases cases and non-cases • See pp. 23 – 26 for examples of See pp. 23 – 26 for examples of

interviewsinterviews

Snow’s Map of Golden Snow’s Map of Golden Square Cholera Outbreak Square Cholera Outbreak

(Fig 1.14)(Fig 1.14)• Cases more likely to live near Cases more likely to live near

Broad St. pump Broad St. pump • Exceptions: no cases in Brewery Exceptions: no cases in Brewery

and few cases in Workhouseand few cases in Workhouse• {Paste section of map here}{Paste section of map here}

Exposure to Broad St. Exposure to Broad St. Pump WaterPump Water

• Case-control studies measure frequency Case-control studies measure frequency of exposure (not frequency of disease)of exposure (not frequency of disease)

• Consumption (exposure) frequent in Consumption (exposure) frequent in casescases• 61 cases – exposure confirmed61 cases – exposure confirmed• 6 cases – non-exposed6 cases – non-exposed• 6 cases – equivocal6 cases – equivocal

• Exposure rare in non-casesExposure rare in non-cases• Exposure more frequent in cases than Exposure more frequent in cases than

controls controls

Removal of Broad Street Removal of Broad Street Pump Handle Pump Handle

• Snow supported his [good] theory Snow supported his [good] theory with high quality datawith high quality data

• But how did he convince the But how did he convince the Guardians of the Golden Square Guardians of the Golden Square area to remove the pump handle?area to remove the pump handle?

2020thth Century Century EpidemiologyEpidemiology

(p. 26)(p. 26)• Addressing the chronic disease Addressing the chronic disease

associated with epidemiologic associated with epidemiologic TransitionTransition

• Illustrative examples Illustrative examples • British Doctors Study (Doll & Hills British Doctors Study (Doll & Hills

studies of the effects of smoking)studies of the effects of smoking)• Framingham Heart Study (risk factors Framingham Heart Study (risk factors

for heart disease, many investigators)for heart disease, many investigators)