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DISEASE DETECTIVES – PART ONEBACKGROUND & SURVEILLANCEClinical Approach vs. Public Health Approach to Health Care·Clinical Approach – primary role is diagnosis and treatment of illness in individuals, preventivemedicine (e.g., immunizations, smoking cessation, obesity counselling and other behavioral/lifestyleconcerns) has only been addressed recently – focus remains on the individuals.·Public Health Approach – primary role is in control and prevention of disease in populations orgroups of individuals, some activities (e.g., diagnosing cases associated with outbreaks and treatingpersons with communicable diseases such as tuberculosis or syphilis) may overlap with those in clinicalmedicine.·There are notable differences between the two disciplines of clinical medicine and public health.Public HealthClinical MedicinePrimary osisHealth PromotionTreatmentWhole CommunityWhole PatientParadigmInterventions aimed at Environment, Medical CareHuman Behavior and Lifestyle, andMedical CareOrganizational Lines ofSpecializationAnalytical (Epidemiology);Organ (Cardiology);Setting and Population(Occupational Health);Patient Group (Pediatrics);Substantive Health Problem(Nutrition);Etiology, Pathophysiology(Oncology, InfectiousDisease)Skills in Assessment, PolicyDevelopment, and AssuranceTechnical Skill (Radiology)[Adapted from: Fineberg, Harvey, MD, PhD, Dean, Harvard University School of Public Health,1990. Traditional Distinctions Between Public Health and Medicine. Table 5-1, Who Will Keepthe Public Healthy? Educating Public Health Professionals for the 21st Century. Institute ofMedicine.1

Selected History of Epidemiology and Population HealthCirca 400 B.C. - Epidemiology's roots are nearly 2500 years old. Hippocrates attempted to explain diseaseoccurrence from a rational rather than a supernatural viewpoint.1662 - John Graunt, a London haberdasher and councilman published a landmark analysis of mortalitydata in 1662.1740’s James Lind – designed first experiment to use a concurrently treated control group while studyingscurvy – determined limes could prevent scurvy – British sailors became known as “limeys”1790’s-Edward Jenner developed the small pox vaccine using clinical trials using cowpox1800 - William Farr built upon Graunt's work by systematically collecting and analyzing Britain'smortality statistics. Farr, considered the father of modern vital statistics and surveillance, developedmany of the basic practices used today in vital statistics and disease classification.1849-54-John Snow the “father of field epidemiology.” formed and tested hypothesis on the origin ofcholera as waterborne transmission in London - one of the first studies in analytic epidemiology1880’s- Louis Pasteur recognized the bacterial cause and developed a vaccine for anthrax1843-1910-Robert Koch – formalized standards (postulates) to identify organisms with infectious diseases1910's - Flu pandemic1920 - Joseph Goldberger published a descriptive field study showing the dietary origin of pellagra1940's - Fluoride supplements added to public water supplies in randomized community trials1949 - Initiation of the Framingham study of risk factors for cardiovascular disease1950 - Epidemiological studies link cigarette smoking and lung cancer, demonstrating the power of casecontrol study design1954 - Field trial of the Salk polio vaccine - the largest formal human experiment1959 - Mantel and Haenszel develop a statistical procedure for stratified analysis of case-control studies1960 - MacMahon published first epidemiologic text with a systematic focus on study design1964 - US Surgeon General's Report on Smoking and Health establish criteria for evaluation of causality1970's - Large community based trials implemented, such as North Karelia and Stanford ThreeCommunities; worldwide eradication of smallpox1980's - Chronic disease, injury and occupational epidemiology; HIV epidemic1990's – Edward Sydenstricker (early 1900’s) became a pioneer public health statisticianBehavioral risk factor epidemiology; prevention of adverse health outcomes through polices andregulations; national programs in breast and cervical cancer prevention; tobacco epidemiology;emerging infectious diseases; criticism of epidemiology for being inconsequential ('small' riskratios); standardization of surveillance methods; Mad cow disease (BSE) in England and Europe;variant Creutzfeld-Jacob disease; aging of USA; disaster epidemiology2000's - Genetic and molecular epidemiology; health disparities; racialism; HIPAA in the USA; West NileVirus - 9/11 - bioterrorism; anthrax and smallpox threat and vaccinations - SARS, quarantines and public health law; and world-wide epidemiology; BSE in Canada - SARS recurrence; BSE in USA; flu epidemic - H1N1 pandemic2

Main Components of Public Health Approach – Problem to ResponsePublic health problems are diverse and can include:· infectious diseases· chronic diseases· emergencies· injuries· environmental health problems· other health threats(from CDC-Public Health 101 Series)Surveillance- What is the problem or Is there a problem?Risk Factor Identification- What is the cause?Intervention Evaluation- What works?Implementation-How do you do it?Key Terms in Public Healtho clinical care: prevention, treatment, and management of illness and the preservation of mental andphysical well-being through the services offered by medical and allied health professions; alsoknown as health care.o determinant: factor that contributes to the generation of a trait.o epidemic or outbreak: occurrence in a community or region of cases of an illness, specific healthrelated behavior, or other health-related event clearly in excess of normal expectancy. Both termsare used interchangeably; however, epidemic usually refers to a larger geographic distribution ofillness or health-related events.o health outcome: result of a medical condition that directly affects the length or quality of aperson’s life.3

Health Determinants····Genes and biologyHealth behaviorsSocial and societal characteristicsAccess to and use of health services and medical care(from CDC-Public Health 101 Series)·····This chart is an estimate of how these four major determinants influence health at the population level.Trillions of dollars are spent on health care, yet it only determines about 25% of our health.The remaining 75% of what determines our health as a population is our total environment or ecology,including the social environment in which we live, plus our health behaviors and to a lesser extent, ourgenes and biology.An example of the role these determinants play in our daily lives is through nutrition and physicalactivity. Both are essential elements in producing optimal health and should be viewed in the context ofsuch environmental factors aso social and cultural norms that influence food choices and physical activity,o environmental characteristics, such as availability (lack of healthy food, open space for exercise, orsafety in urban neighborhoods), ando sector influences, such as the marketing of processed food.All of these factors influence our individual choices, which in turn, influence our overall health.4

(from CDC-Public Health 101 Series)Major Types of Public Health Issues in the USThe CDC’s Prevention Status Report lists the 10 most important public health problems and concerns are(listed alphabetically):Health Impact Pyramid··········Alcohol-related harmsFood safetyHealthcare-associated infectionsHeart disease and strokeHIVMotor vehicle injuryNutrition, physical activity andobesityPrescription drug overdoseTeen pregnancyTobacco useFrieden TR. Framework for public health action: the healthimpact pyramid. Am J Public Health ;100:590–5.5

Epidemiology and Its Role in Public HealthEpidemiology – the disease detectives who work to solve public health issues· Definition-the study of the distribution and determinants of health-related states or events in specifiedpopulations, and the application of this study to the control of health problem· Purposes of Epidemiology in Public Health Practiceo Determine the agent, host, and environmental factors that affect healtho Determine the relative importance of causes of illness, disability, and deatho Identify those segments of the population that have the greatest risk from specific causes of ill healtho Evaluate the effectiveness of health programs and services in improving population health· Types of disease agents – biologic, physical, and chemicalSteps in Solving Health ProblemsStep 1-Collect Data – Surveillance, determine Time/Place/Person triadStep 2- Assessment- InferenceStep 3- Hypothesis testing – Determine how and whyStep 4- Action-InterventionDescriptive Epidemiology involves identifying to the time,place, and the person involved in the onset of the healthrelated event.Analytical Epidemiology is mainly concerned with findingthe causes of the health-related event and to identify theinterventions of the health problem.CDC - Public Health 101 SeriesDescriptive vs Analytical EpidemiologyDescriptive Epidemiology refers to the studiesthat generate hypotheses and answer the questionswho, what, when and where of the disease orAnalytic Epidemiology refers to the studiesthat are conducted to test for hypotheses and togenerate conclusions on the particular disease.infection.HypothesisDescriptive epidemiology is able to generate aAnalytic epidemiology is able to conduct a testhypothesis.for the hypothesis.InterventionsIntervention studies are not performed inInterventions are analyzed in analyticdescriptive epidemiology.epidemiology.6

CDC - Public Health 101 Series··In an Experimental Study, the investigators can control certain factors within the study from thebeginning. An example of this type is a vaccine efficacy trial that might be conducted by the NationalInstitutes of Health. In such a trial, the investigators randomly control who receives the test vaccine andwho does not among a limited group of participants; they then observe the outcome to determine if itshould to be used more widely.In an Observational Study, the epidemiologist does not control the circumstances. These studies can befurther subdivided into descriptive and analytic.o In a Descriptive Study, the epidemiologist collects information that characterizes and summarizesthe health event or problem.o In the Analytic Study, the epidemiologist relies on comparisons between different groups todetermine therole ofdifferentcausativeconditions orrisk factors.7

Basic Epidemiology Terms – Disease FrequencyooooooooooEndemic – disease or condition present among a population at all timesOutbreak – (localized epidemic) – more cases of a particular disease than expected in a given areaor among a specialized group of people over a particular period of time.Epidemic – large numbers of people over a wide geographic area affected.Pandemic -An epidemic occurring over a very wide area (several countries or continents) andusually affecting a large proportion of the population.Cluster –an aggregation of cases over a particular period esp. cancer & birth defects closelygrouped in time and space regardless of whether the number is more than the expected number.(often the expected number of cases is not known.)Sporadic – a disease that occurs infrequently and irregularlyrisk - The probability that an individual will be affected by, or die from, an illness or injury withina stated time or age span.rate – number of cases occurring during a specific period;always dependent on the size of the population during thatperiod.ratio – value obtained by dividing one quantity by another – aratio often compares two rates.proportion – the comparison of a part to the whole as the number of cases divided by the totalpopulation – does not have a time dimension, It can be expressed as a decimal, a fraction, or apercentage.Symbiotic Relationships between organisms:o Normal flora – Many microbes have a positive symbiotic relationship with other organisms.Mutualism – both organisms benefit.o Commensalism – one organisms and the other is not harmed or helped.o Parasitism is the condition (one organism is helped and the other is harmed) which takes placewhen humans are invaded by infectious microbes. A parasite-host relationship is created. Theparasite is often called the infectious agent.8

Natural History and Spectrum of Disease(CDCSelf-Study Course SS1978 Lesson 1)Natural history of disease refers to the progression of a disease process in an individual over time, in theabsence of treatment.Many, if not most, diseases have a characteristic natural history, although the time frame and specificmanifestations of disease may vary from individual to individual and are influenced by preventive andtherapeutic measures.Natural History of Disease TimelineTimeline shows state of susceptibility, exposure, subclinical disease in which pathologic changes takesplace, onset of symptoms, followed by usual time of diagnosis, clinical disease, followed by recovery,disability, or death.The process begins with the appropriate exposure to or accumulation of factors sufficient for the diseaseprocess to begin in a susceptible host. For an infectious disease, the exposure is a microorganism. Forcancer, the exposure may be a factor that initiates the process, such as asbestos fibers or components intobacco smoke (for lung cancer), or one that promotes the process, such as estrogen (for endometrialcancer).After the disease process has been triggered, pathological changes then occur without the individualbeing aware of them.This stage of subclinical disease, extending from the time of exposure to onset of disease symptoms, isusually called the incubation period for infectious diseases, and the latency period for chronicdiseases.During this stage, disease is said to be asymptomatic (no symptoms) or inapparent. This period may beas brief as seconds for hyperse