epidemiology who gets disease and why for health care providers

EPIDEMIOLOGYEPIDEMIOLOGY

WHO GETS DISEASE AND WHY

FOR HEALTH CARE PROVIDERSFOR HEALTH CARE PROVIDERS


DEFINITION:DEFINITION:The study of what is upon the peopleThe study of what is upon the people

EpiEpi-upon + -upon + DemosDemos-people +-people + logos logos-study -study ofof

Studies the factors affecting the Health and Studies the factors affecting the Health and illness of a populationillness of a population

Describes quantities and postulates causal Describes quantities and postulates causal mechanisms for health phenomena in a mechanisms for health phenomena in a population (population (Friis and Sellers 1999)Friis and Sellers 1999)


Disease Mortality Hospitalization Disability Quality of Life Health status

Important Issues that Epidemiology can address

It’s not just disease!

EPIDEMIOLOGY: HistoryEPIDEMIOLOGY: History

HippocratesHippocrates::• First known to examine First known to examine

relationships between relationships between occurrence of disease occurrence of disease and environmental and environmental influencesinfluences

• Coined terms: Epidemic Coined terms: Epidemic and endemicand endemic

Ancient Ancient GreeksGreeks


AvicennaAvicenna::• Discovered Discovered

contagious Nature of contagious Nature of diseasedisease

• Introduced methods Introduced methods of quarantine and of quarantine and risk factor analysisrisk factor analysis

Medieval Islamic Medieval Islamic worldworld


Mid 16Mid 16thth Century CenturyGirolamo FracastoroGirolamo Fracastoro::• First to propose disease First to propose disease

caused by small living caused by small living particlesparticles

• First to promote personal First to promote personal and environmental and environmental hygienehygiene


Mid 19Mid 19thth Century Century

John SnowJohn Snow::• Identified cause of Identified cause of

Outbreak of cholera Outbreak of cholera in London 1854 in London 1854

• Event Led to science Event Led to science of Epidemiologyof Epidemiology


Mid 20Mid 20thth century century

Doll and HillDoll and Hill:: Published results from Published results from

“British Doctors Study” “British Doctors Study” showing link of tobacco showing link of tobacco smoking to lung cancersmoking to lung cancer

EPIDEMIOLOGY: GoalsEPIDEMIOLOGY: Goals

DescribeDescribe the health status of the health status of populationspopulations

ExplainExplain the etiology of disease the etiology of diseasePredictPredict disease occurrence disease occurrence

Look for causal Look for causal relationshipsrelationships


Disease does NOT occur randomlyDisease does NOT occur randomlyAppears in patterns that reflect Appears in patterns that reflect

underlying factors that can be underlying factors that can be determineddetermined

Basic PremiseBasic Premise


Use data to:Use data to:Generate or expand theoryGenerate or expand theoryTest hypothesisTest hypothesisMake educated assertions about: Make educated assertions about:

which relationships are causal which relationships are causal how are they causalhow are they causal

Basic PremiseBasic Premise


Most causal propositions cannot be proven

• One cause – one effect too simplisticOne cause – one effect too simplistic• Correlation does not imply causationCorrelation does not imply causation• Most outcomes are multi-factorialMost outcomes are multi-factorial

(Rothman and Greenland 2005)(Rothman and Greenland 2005)

Causal InferenceCausal Inference

EPIDEMIOLOGY: Descriptive EPIDEMIOLOGY: Descriptive StudiesStudies

Looks at — Time, Place, Looks at — Time, Place, PersonPerson Age, sex, race and ethnicity, Age, sex, race and ethnicity,

religion, education, occupation, religion, education, occupation, area of the world or country one area of the world or country one lives in, historical-temporal lives in, historical-temporal relationships and other factors relationships and other factors that can define a group or that can define a group or “cohort.”“cohort.”


Looks only at identification of Looks only at identification of diseasedisease

Concerned with characterizing Concerned with characterizing the amount and distribution of the amount and distribution of a disease within a populationa disease within a population

Cannot be used for causalityCannot be used for causality


1.1. Permit evaluation of trends in health and disease Permit evaluation of trends in health and disease and comparisons among countries and sub-groups and comparisons among countries and sub-groups of countries including monitoring disease and of countries including monitoring disease and identification of emerging problems.identification of emerging problems.

2.2. Provide a basis for planning, provision and Provide a basis for planning, provision and evaluation of health services; data needed for evaluation of health services; data needed for efficient allocation of resources.efficient allocation of resources.

3.3. Identification of problems that can be studied with Identification of problems that can be studied with analytic methods and to suggest areas that may analytic methods and to suggest areas that may be helpful for investigations.be helpful for investigations.

Three Broad GoalsThree Broad Goals


Case report – describes Case report – describes characteristics and/or response to characteristics and/or response to treatment of an individual patienttreatment of an individual patient

Case series – describes Case series – describes characteristics and/or response to characteristics and/or response to treatment of a number of patientstreatment of a number of patients

Case report (series)Case report (series)

Ex. The HIV/AIDS epidemic—Ex. The HIV/AIDS epidemic—descriptive data indicated the descriptive data indicated the emergence of the epidemic, was emergence of the epidemic, was used in learning how to allocate used in learning how to allocate beds and hospital resources, beds and hospital resources, spurred etiological studies into spurred etiological studies into why i.v. drug users and gay males why i.v. drug users and gay males were more likely to develop the were more likely to develop the disease than other groups.disease than other groups.


EPIDEMIOLOGY: Observational EPIDEMIOLOGY: Observational StudiesStudies

An empiric comparison of treated and control groups in which it is not feasible to use controlled experimentation, in the sense of being able to impose the procedures or treatments whose effects it is desired to discover, or to assign subjects at random to different procedures. (Rosenbaum 2005)

NON-RANDOMIZED STUDY


Used when a randomized experiment Used when a randomized experiment may be impractical or would violate may be impractical or would violate ethicalethical standards standards

Ex. Exploring a causal link between Ex. Exploring a causal link between tobacco smoking and the incidence of tobacco smoking and the incidence of breast cancer. In a hypothetical breast cancer. In a hypothetical controlled experiment, a large subject controlled experiment, a large subject pool of non-smoking women would be pool of non-smoking women would be divided randomly into a treatment divided randomly into a treatment group (smokers) and a control group group (smokers) and a control group (non-smokers), and then regular cancer (non-smokers), and then regular cancer screenings for both groups would be screenings for both groups would be conducted. conducted.


Looks at the difference between Looks at the difference between one group who has a disease or one group who has a disease or develops a disease and one group develops a disease and one group that did notthat did not

Typically, a case is matched to a Typically, a case is matched to a control who has similar control who has similar demographic characteristics.demographic characteristics. Some believe this is the “mainstay” Some believe this is the “mainstay”

of epidemiologic research.of epidemiologic research.

Case Control StudiesCase Control Studies


May represent 80% of May represent 80% of epidemiological studiesepidemiological studies Often poorly designedOften poorly designed

subject to recall bias, selection bias subject to recall bias, selection bias must be carefully matched for location must be carefully matched for location

and other demographic specific and other demographic specific information to be validinformation to be valid

Case Control StudiesCase Control Studies


A group of people A group of people who have who have something in something in commoncommon Called “population Called “population

at riskat risk

Cohort StudiesCohort Studies


Follow a cohort over a period of Follow a cohort over a period of time.time.

Cohort followed through time to Cohort followed through time to assess later outcome statusassess later outcome status may look at one single risk factor or may look at one single risk factor or

exposure for the group and compare exposure for the group and compare incidence rates* or prevalence** within incidence rates* or prevalence** within the group.the group.

* Number of new cases/population* Number of new cases/population

** Total number of cases/population** Total number of cases/population

Cohort StudiesCohort Studies


Looks at prevalence Looks at prevalence A "snapshot" of the frequency and A "snapshot" of the frequency and

characteristics of a condition or characteristics of a condition or disease in a population at a disease in a population at a particular point in timeparticular point in time

Often done because they are not Often done because they are not too expensive and they don’t too expensive and they don’t take too much time.take too much time.

Cross-sectional Cross-sectional StudiesStudies


Repeated observations of the same Repeated observations of the same items over long periods of time - often items over long periods of time - often many decades many decades

Used in psychology to study Used in psychology to study developmental trends across the life developmental trends across the life spanspan

Ex. Framingham Heart Study: 50 years Ex. Framingham Heart Study: 50 years of observation of inhabitants of of observation of inhabitants of Framingham Mass. to monitor Framingham Mass. to monitor cardiovascular disease cardiovascular disease

Longitudinal StudiesLongitudinal Studies

EPIDEMIOLOGY: EPIDEMIOLOGY: DefinitionsDefinitionsEndemic Endemic - disease that is constantly - disease that is constantly

presentpresentEpidemic Epidemic - an unusually high - an unusually high

occurrence of disease that is out of occurrence of disease that is out of proportion to time and placeproportion to time and place

PandemicPandemic - a series of epidemics - a series of epidemics involving several countries or large involving several countries or large segments of the populationsegments of the population

EPIDEMIOLOGY: EPIDEMIOLOGY: DefinitionsDefinitionsOutbreak Outbreak - - suddensudden presence of a presence of a

disease that is not typically seen disease that is not typically seen or of a disease that has never or of a disease that has never been seen. Could represent a been seen. Could represent a seasonal outbreak of a disease seasonal outbreak of a disease that is commonthat is common

Ebola Hemmhoragic Fever or, an influenza Ebola Hemmhoragic Fever or, an influenza outbreak in the U.S.outbreak in the U.S.

EPIDEMIOLOGY: EPIDEMIOLOGY: DefinitionsDefinitionsDeterminants Determinants - - factorsfactors that bring that bring

about, or are capable of bringing about, or are capable of bringing about changes in healthabout changes in health

VectorsVectors – a non- – a non-human source of human source of infection or infection or disease that can disease that can affect humans (ie. affect humans (ie. Insects, dogs, bats, Insects, dogs, bats, etc)etc)

EPIDEMIOLOGY: EPIDEMIOLOGY: DefinitionsDefinitionsMorbidityMorbidity - number of individuals - number of individuals

having a disease per unit having a disease per unit population within a given time. Ex. population within a given time. Ex. 8,000/100,000 or 10/100,0008,000/100,000 or 10/100,000

MortalityMortality - number of deaths - number of deaths attributed to a disease (or, all attributed to a disease (or, all causes) per unit of the population causes) per unit of the population within a given time. (usually per within a given time. (usually per 1,000, per year)1,000, per year)

Infant mortality rate x/1,000 per yearInfant mortality rate x/1,000 per year

EPIDEMIOLOGY: EPIDEMIOLOGY: DefinitionsDefinitionsCountsCounts - simple numbers of people - simple numbers of people

affected or dead ect., to determine affected or dead ect., to determine rates of disease.rates of disease. E.g. number of “cases”E.g. number of “cases”

Rates Rates - frequency of a disease during - frequency of a disease during a time period/unit size of populationa time period/unit size of population Crude birth rate= number of live births per year Crude birth rate= number of live births per year

per 1,000 population per 1,000 population Ex. 1991Ex. 1991

4,111,000/252,688,000(pop)=16.3/1,000 pop4,111,000/252,688,000(pop)=16.3/1,000 pop

EPIDEMIOLOGY: EPIDEMIOLOGY: DefinitionsDefinitions IncidenceIncidence – –number of number of new individualsnew individuals

who contract a disease within a specified who contract a disease within a specified timetime Number of new cases/size of population at riskNumber of new cases/size of population at risk

Incidence rateIncidence rate – incidence/time – incidence/time Measures probability of diseaseMeasures probability of disease

PrevalencePrevalence - - number of number of all individualsall individuals affected by the disease within a specified affected by the disease within a specified time time total number of cases in the population/ the number of total number of cases in the population/ the number of

individuals in the population X 100individuals in the population X 100 used to estimate how common a condition is within a used to estimate how common a condition is within a

population over a certain period of timepopulation over a certain period of time

EPIDEMIOLOGY: EPIDEMIOLOGY: DefinitionsDefinitions

Ex. Ex. If a population initially contains If a population initially contains 1,000 non-diseased persons and 1,000 non-diseased persons and 28 develop a condition over two 28 develop a condition over two years of observation, the years of observation, the incidenceincidence isis 28 cases per 1,000 28 cases per 1,000 persons, i.e. persons, i.e. 2.8%.2.8%. incidence rateincidence rate is 14is 14 cases per 1000 person- cases per 1000 person-years, because the incidence (28 years, because the incidence (28 per 1,000) is divided by the per 1,000) is divided by the number of years (two). number of years (two).

EPIDEMIOLOGY: EPIDEMIOLOGY: DefinitionsDefinitions

Ex. If the condition takes a long Ex. If the condition takes a long time to cure, and time to cure, and if 22 cases were if 22 cases were recorded in year one, but only 6 recorded in year one, but only 6 cases were recorded in year two, cases were recorded in year two, then in then in year oneyear one the condition will the condition will have a have a highhigh prevalenceprevalence and a and a high high incidenceincidence; but in ; but in year twoyear two it will it will have have low incidencelow incidence, and continue , and continue to have to have high prevalencehigh prevalence due to due to long healing timelong healing time

EPIDEMIOLOGY: EPIDEMIOLOGY: Chronic Chronic DiseaseDisease

Chronic disease kills more people Chronic disease kills more people than almost all other causes than almost all other causes combinedcombined

By definition have —By definition have —Prolonged course, does not resolve Prolonged course, does not resolve

spontaneously, usually not spontaneously, usually not communicable, often uncertain communicable, often uncertain etiology, multiple risk factors, long etiology, multiple risk factors, long latency period, associated with latency period, associated with impairment and disability and impairment and disability and incurabilityincurability


Often looks at risk factorsOften looks at risk factors Offices often seen within the public health Offices often seen within the public health

department of the USdepartment of the US Cancer RegistryCancer Registry Breast and Cervical CancerBreast and Cervical Cancer DiabetesDiabetes ArthritisArthritis Tobacco Control and PreventionTobacco Control and Prevention Risk SurveillanceRisk Surveillance OsteoporosisOsteoporosis AsthmaAsthma


A Couple of Chronic Disease FactoidsA Couple of Chronic Disease Factoids

By 2020, non-communicable disease will likely By 2020, non-communicable disease will likely account for 70% of all deaths in account for 70% of all deaths in developingdeveloping countries whereas, today they account for ½.countries whereas, today they account for ½.

Also by 2020, tobacco attributable ds is Also by 2020, tobacco attributable ds is expected to exceed that caused by any single expected to exceed that caused by any single ds.ds.

--Epidemiology--Epidemiology. (2000) Gordis, L. Philadelphia. W.B. Saunders, 2. (2000) Gordis, L. Philadelphia. W.B. Saunders, 2ndnd Ed. p.58-9Ed. p.58-9..

EPIDEMIOLOGY: Healthy People 2010 EPIDEMIOLOGY: Healthy People 2010 goalsgoals

1.1. Access to quality health care servicesAccess to quality health care services2.2. Arthritis, osteoporosis, Arthritis, osteoporosis, chronic back conditionschronic back conditions3.3. CancerCancer4.4. Chronic kidney diseaseChronic kidney disease5.5. DiabetesDiabetes6.6. Disability and secondary conditionsDisability and secondary conditions7.7. Educational & community-based programsEducational & community-based programs8.8. Environmental health Environmental health 9.9. Family PlanningFamily Planning10.10. Food SafetyFood Safety11.11. Health communicationHealth communication12.12. Heart disease/strokeHeart disease/stroke13.13. HIVHIV14.14. Immunization/Infectious diseaseImmunization/Infectious disease15.15. Injury and violence preventionInjury and violence prevention

EPIDEMIOLOGY: Leading causes of deathEPIDEMIOLOGY: Leading causes of death

1.1. Heart diseaseHeart disease2.2. *Cancer*Cancer3.3. StrokeStroke4.4. COPDCOPD5.5. InjuriesInjuries6.6. DiabetesDiabetes7.7. Flu/PneumoniaFlu/Pneumonia8.8. Alzheimer’sAlzheimer’s9.9. Kidney diseaseKidney disease10.10. SepticemiaSepticemia*Cancer rates have remained *Cancer rates have remained

basically stable for over 20 basically stable for over 20 years but dropped 10%years but dropped 10%

from 1990-2002.from 1990-2002.

Source: Chartbook on Trends in the Health of Americans, Source: Chartbook on Trends in the Health of Americans, CDCCDC, 2005, 2005

EPIDEMIOLOGY: Disease of EPIDEMIOLOGY: Disease of LifestyleLifestyle

Regardless of what you may hear:Regardless of what you may hear:

Virtually Virtually NONO ONEONE (in medicine, public health, (in medicine, public health, government or otherwise) IS SUGGESTING A government or otherwise) IS SUGGESTING A GENETICGENETIC CAUSE FOR OBESITY CAUSE FOR OBESITY

It is all about It is all about LifestyleLifestyle for almost for almost everyone!everyone!

‘‘I have a glandular condition that my mother I have a glandular condition that my mother had’had’

A word about the most common causes of A word about the most common causes of death in America…….death in America…….

EPIDEMIOLOGY: Breslow’s 7 Healthy EPIDEMIOLOGY: Breslow’s 7 Healthy HabitsHabits

Studied health practices of citizens in Alameda Studied health practices of citizens in Alameda County, California over 30 years. (Longitudinal)County, California over 30 years. (Longitudinal)

1.1. Avoid excessive alcoholAvoid excessive alcohol2.2. Don’t smoke (or use tobacco)Don’t smoke (or use tobacco)3.3. Don’t become obeseDon’t become obese4.4. ““Sleep 7-8”Sleep 7-8”5.5. Get adequate physical activityGet adequate physical activity6.6. Don’t eat between mealsDon’t eat between meals7.7. Eat breakfast!Eat breakfast!

Health practices and disability: some evidence Health practices and disability: some evidence from Alameda County. (1993) Breslow & Breslow. from Alameda County. (1993) Breslow & Breslow.

Preventive Medicine Preventive Medicine 22, 86-9522, 86-95

Use of EpidemiologyUse of Epidemiology

• In the United States, the National Center In the United States, the National Center for Health Statistics is a data source for for Health Statistics is a data source for information on health and diseaseinformation on health and disease

http://http://www.cdc.gov/nchswww.cdc.gov/nchs

• Globally, the World Health Organization Globally, the World Health Organization is a data source for information on is a data source for information on health and diseasehealth and disease

http://www.who.inthttp://www.who.int

Epidemiology Super-course Epidemiology Super-course sitesite

http://www.pitt.edu/~super1http://www.pitt.edu/~super1

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epidemiology who gets disease and why for health care providers

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