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Foundations of Epidemiology

Chapter 1

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What is Health?

The absence of illness

6 dimensions of health

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What are the 6 Dimensions of Health?Physical Ability of the human body to function properly; includes physical fitness and activities of

daily living.

Social Ability to have satisfying relationships; interaction with social institutions and societal

mores.

Mental Ability to think clearly, reason objectively, and act properly.

Emotional Ability to cope, adjust and adapt; self-efficacy and self-esteem.

Spiritual Feeling as if part of a greater spectrum of existence; personal beliefs and choices.

Environmental Comprised of external factors (i.e., ones surroundings such as habitat or occupation) and

internal factors (i.e., ones internal structure such as genetics).

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What is Public Health?Public health is the science and art of

promoting health and extending life on thepopulation level.

Public health is concerned with threats to

health in the population (a group of peoplesharing one or more characteristics).

The mission of public health is to ensureconditions that promote the six dimensions

of health in the population as a whole.

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What is the Meaning of Population?Population refers to a collection of individuals thatshare one or more observable personal orobservational characteristics from which data may becollected and evaluated.

SocialEconomic

Family (marriage and divorce)

Work and labor force

Geographic factors

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How does Public Health Relate toEpidemiology?There are many subfields of publichealth, including epidemiology,

biostatistics, and health services.Because of its central role in publichealth, epidemiology is commonly

referred to as the foundation ofpublic health.

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What is Epidemiology?Epidemiology is the study of the distributionand determinants of health-related states or

events in human populations, and theapplication of this study to prevent and controlhealth problems.

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What is Epidemiology?The word epidemiology is based on the Greekwords:epiprefix meaning on, upon, or befall

demosroot meaning the people logossuffix meaning the study

In other words, epidemiology is the study of whatbefalls the population.

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Key Terms in the DefinitionStudy - Epidemiology involves soundmethods of scientific investigation.

Methods rely on careful observation and

the use of valid comparison groups todetermine whether the observed healthevents differ from what might be

expected.

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Key Terms in the DefinitionDistributionStudy of frequency and pattern of healthevents in the population

Frequency

number, and number inrelation to the population

Pattern the health-related state or eventby person, place, and time characteristics

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Key Terms in the Definition

Determinants

Search for causes and other factors ofhealth-related states or events.

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Key Terms in the DefinitionHealth-related states or eventsDisease states cholera, influenza, pneumonia, mental illness

Conditions associated with healthphysical activity, nutrition, environmental poisoning,seat belt use, and provision and use of healthservices

Events injury, drug abuse, and suicide

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Key Terms in the DefinitionApplication of this study to preventand control health problems.

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Why is Epidemiology Considered by Many tobe the Foundation of Public Health?

Because of its central role in carrying out thethree core public health functions:

1. The assessment and monitoring of the health of communitiesand populations at risk to identify health problems and priorities.

2. The formulation of public policies designed to solve identifiedlocal and national health problems and priorities.

3. To assure that all populations have access to appropriate andcost-effective care, including health promotion and diseaseprevention services, and evaluation of the effectiveness of thatcare.

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The Epidemiologic FocusClinical focus vs. epidemiologicfocus

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Epidemiology and the Scientific MethodEpidemiology uses the scientificmethod to describe and analyze

health-related states or events.

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What is the Scientific Method?The scientific method involves using appropriate studydesigns and statistical techniques for investigating anobservable occurrence and acquiring new knowledge.

The health problemHypotheses

Statistical testing

Interpretation

Dissemination

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Study Designs in EpidemiologyDescriptive epidemiology

Involves study designs used to answer: Who?What? When? Where?

Analytic epidemiologyInvolves study designs used to answer: Why?How?

Later chapters will focus on describing thesestudy designs.

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The Importance of Descriptive EpidemiologyA means to characterizing thedistribution of health-related states orevents by

Person who?

Place where?

Time when?

Clinical criteria what?

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The Importance of Analytic EpidemiologyA means to identifying and quantifyingassociations, testing hypotheses, and

supporting statements about causalityExplains why and how health-related statesor events occur

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Selected Activities Performed inEpidemiology Identifying risk factors for disease, injury, and death

Describing the natural history of disease

Identifying individuals and populations at greatest riskfor disease

Identifying where the public health problem is greatest

Monitoring diseases and other health-related eventsover time

Evaluating the efficacy and effectiveness of preventionand treatment programs

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Epidemiology in Public Health Practice andIndividual Decision MakingEpidemiological findings contribute to

Preventing and controlling disease, injury,

disability, and deathHow?

By providing information leading to informedpublic health policy and planning, as well asindividual health decision making

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Selected Types of EpidemiologicInformationPublic health assessment

Causes of disease

Completing the clinical picture

Program evaluation

EfficacyEffectiveness

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Questions that Need Epidemiology

Diagnosis Is there such a problem as myalgic encephalitis?

Is prostate specific antigen a good test forprostate cancer?

CausesWhy did this patient suffer a stroke?

Is obesity the cause of metabolic syndrome?

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Questions that Need EpidemiologyTreatment Is this the best treatment for Parkinson's disease?

Is my surgery as good as that of everyone else?

PrognosisWhat are the chances of a recurrent heart attack?

How long will this knee joint prosthesis last?

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Questions that Need EpidemiologyHealth promotion and protection

Do current school meals harm children's futurehealth?

Will the Irish smoking ban in public places workbetter than the English policy?

Health and disease surveillance

Why are there 10 fold international differencesin suicide rates?

When will the next influenza pandemic occur?

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Questions that Need EpidemiologyHealth inequalities

Why should life expectancy be nearly five

years lower in unskilled manual workers?Do health services reduce or increase healthinequalities?

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Epidemic Endemic and PandemicEpidemic Health-related state or event in adefined population above the expected over agiven period of time

Endemic

Persistent, usual, expected health-related state or event in a defined populationover a given period of time

Pandemic Epidemic affecting a large number

of people, many countries, continents, or regions

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Common Source Propagatedand Mixed EpidemicsCommon source

Point

Intermittent

ContinuousPropagated

Spread from person to person

Mixed epidemicsA mixture of common source and mixed

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Common SourceTend to result in more cases occurringmore rapidly and sooner than host-to-hostepidemics.

Identifying and removing exposure to thecommon source typically causes theepidemic to rapidly decrease.

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Common SourceExamples

anthrax, traced to milk or meat from infected

animalsbotulism, traced to soil-contaminated food

cholera traced to fecal contamination of foodand water

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PropagatedArise from infections being transmitted from oneinfected person to another

Transmission can be through direct or indirectroutes

Host-to-host epidemics rise and fall more slowlythan common source epidemics

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Mixed EpidemicsOccurs when a common source epidemic is followedby person-to-person contact and the disease is

spread as a propagated outbreak

Example

Shigellosis occurred among a group of3000 women attending a music festival. Over thenext few weeks, subsequent generations of shigella

cases spread by person-to-person transmission from

festival attendees.

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Disease TransmissionDisease transmission usually occurs by

direct, person-to-person contact

(e.g., STDs)

fomite-borne (e.g., Hepatitis A spread by acontaminated eating utensil)

vehicle-borne (e.g., HIV/AIDS spread through needlesharing drug users)

vector-borne (e.g., Malaria spread throughmosquitoes)

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Accurate Assessment Requires aStandard Case DefinitionA standard set of criteria, or casedefinition, assures that cases areconsistently diagnosed, regardless ofwhere or when they were identified andwho diagnosed the case

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Concepts and Principles of Case asUsed in EpidemiologyAcase is a person who has beendiagnosed as having a disease, disorder,injury, or condition

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Primary Case Index CaseThe first disease case in the population isthe primary case.

The first disease case brought to theattention of the epidemiologist is the indexcase.

The index case is not always the primary

case.

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Secondary CaseThose persons who become infected andill after a disease has been introducedinto a population and who become

infected from contact with the primarycase

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Different Levels of DiagnosisAs more information (such as laboratory results)becomes available to the physician, he or shegenerally upgrades the diagnosis. When all

criteria are met and they meet the case definition,the case is classified as a confirmed case.

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Epidemiology Triangle for InfectiousDisease

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Triangle is Based on the CommunicableDisease ModelShows the interaction and interdependence of agent,host, environment, and time as used in theinvestigation of diseases and epidemics.Agent is the cause of the disease

Host is an organism, usually a human or an animal, that harbors a diseaseEnvironment includes those surroundings and conditions external to the human or

animal that cause or allow disease transmission

Time accounts for incubation periods, life expectancy of the host or the pathogen,and duration of the course of the illness or condition.

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Stopping an EpidemicAn epidemic can be stopped when one of theelements of the triangle is interfered with,altered, changed, or removed from existence,

so that the disease no longer continues alongits mode of transmission and routes of infection

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Some Disease Transmission ConceptsFomites

Objects such as clothing, towels, and utensilsthat may harbor a disease agent and are

capable of transmitting it; usually used in theplural

Example transmission of cutaneousanthrax from drums to an individual

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VectorAn invertebrate animal (e.g., tick, mite, mosquito,bloodsucking fly) capable of transmitting an infectiousagent among vertebrates

Can spread an infectious agent from an infected animalor human to other susceptible animals or humansthrough its waste products, bite, body fluids, orindirectly through food contamination

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PlagueYersinia pestis (the bacteria that causes plague)is found in animals throughout certain parts of theworld, most commonly in rats, but occasionally inother wild animals, such as prairie dogs. Plaguetransmission from these infected animalsgenerally occurs in one of three ways:

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PlagueBites from infected rodent fleas (85%)Direct contact with infected tissue or bodilyfluids

For example, people can become directlyinfected with plague by handling infectedrodents, rabbits, or wild carnivores that prey onthese animals when plague bacteria enter

through the person's skin.Inhaling infected droplets.

http://plague.emedtv.com/yersinia-pestis/plague-bacteria.html

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ReservoirThe habitat (living or nonliving) on which aninfectious agent lives, grows, multiplies, and is

dependent on for its survival in natureHumans often serve as both reservoir and host

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ZoonosisWhen an animal transmits a disease to ahuman

Examples

rabies, Rocky Mountainspotted fever, shigellosis

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CarrierA carriercontains, spreads, or harbors aninfectious organism

Example Typhoid Mary

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Modes of Disease TransmissionDirect transmission direct physical contactsuch as touching with contaminated hands,skin-to-skin contact, kissing, or sexual

intercourse

Indirect transmission occurs whenpathogens or agents are transferred or carried

by some intermediate item, organism, means,or process to a susceptible host, resulting indisease

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Advanced Epidemiology Triangle forChronic Diseases and Behavioral Disorders

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Three Levels of Prevention Used inPublic Health and EpidemiologyPrimary prevention (occurs prior to exposure)

Immunization

Sanitation

Education

Media campaigns

Warning labels

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Active Primary PreventionRequires behavior change on part of subject

Wearing protective devises

Health promotionLifestyle changes

Community health education

Ensuring healthy conditions at home, schooland workplace

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Passive Primary PreventionDoes not require behavior change

Vitamin fortified foods

Fluoridation of public water supplies

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Secondary PreventionOccurs to reduce the progress of disease

The disease already exists in the person

Cancer screening cancer already present.

The goal is to detect the cancer before clinicalsymptoms arise in order to improve prognosisand prevent conditions from progressing andfrom spreading

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Tertiary PreventionTo reduce the limitation of disability from diseaseThe disease has already occurred

Physical therapy for stroke victims

Halfway houses for recovering alcoholicsShelter homes for the developmentallydisabled

Fitness programs for heart attack patients