Chapter 1The History and Scope of Epidemiology Learning Objectives • Define the term epidemiology • Define the components of epidemiology (determinants, distribution, morbidity, and mortality) • Name and describe characteristics of the epidemiologic approach • Discuss the importance of Hippocrates’ hypothesis and how it differed from the common beliefs of the time • Discuss Graunt’s contributions to biostatistics and how they affected modern epidemiology • Explain what is meant by the term natural experiments, and give at least one example 2006 Outbreak of Escherichia coli • Outbreak during late summer and fall of 2006 • Affected 199 persons and caused 3 deaths • Caused 102 (51%) of ill persons to be hospitalized • A total of 31 patients (16%) were afflicted with hemolytic-uremic syndrome (HUS) • Spread across 26 states • Fresh spinach linked to the outbreak Epidemiology Defined • Epidemiology derives from "epidemic," a term which provides an immediate clue to its subject matter. Epidemiology originates from the Greek words, epi (upon) + demos (people) + logy (study of). morbidity. .Definition of Epidemiology • Epidemiology is concerned with the distribution and determinants of health and diseases. injuries. and mortality in populations. • Epidemiologic studies are applied to the control of health problems in populations. disability. Key Aspects of This Definition • • • • • Determinants Distribution Population Health phenomena Morbidity and mortality . Determinants • Factors or events that are capable of bringing about a change in health. . sedentary lifestyle. or high-fat diet .Examples of Determinants – Biologic agents--bacteria – Chemical agents--carcinogens – Less specific factors--stress. drinking. --Legionnaires’ disease in New York City • Red Spots on Airline Flight Attendants-dye from life vests • Bioterrorism-Associated Anthrax Cases .The Search for Determinants • Anthrax outbreak • Outbreak of Fear--Ebola virus in Kikwit. Zaire • Fear on Seventh Ave. Connecticut. • Contaminated mail linked to some of the cases. • Additional cases. . New Jersey. reported in New York.Bioterrorism-Associated Anthrax Cases • Index case reported in Florida. including fatal cases. Distribution • Frequency of disease occurrence may vary from one population group to another. . .Disease Distribution Examples • Hypertension more common among young black men than among young white men. • Coronary heart disease occurrence differs between Hispanics and non-Hispanics. not individuals. • The epidemiologic description indicates variation by age groups. geographic location.Population • Epidemiology examines disease occurrence among population groups. time. • Epidemiology is often referred to as population medicine. . and other variables. suicide. drug addiction . injury.Health Phenomena • Epidemiology investigates many different kinds of health outcomes: – Infectious diseases – Chronic diseases – Disability. limitation of activity – Mortality – Active life expectancy – Mental illness. • Note that most measures of morbidity and mortality are defined for specific types of morbidity or causes of death.Morbidity and Mortality • Morbidity--designates illness. . • Mortality--refers to deaths that occur in a population or other group. • To control the occurrence of disease. • To explain the etiology of disease.Aims and Levels • To describe the health status of populations. • To predict the occurrence of disease. . Foundations of Epidemiology • • • • Interdisciplinary Methods and procedures—quantification Use of special vocabulary Epidemic frequency of disease . microbiology. . genetics. pathology.Epidemiology Is Interdisciplinary • Epidemiology is an interdisciplinary field that draws from biostatistics and the social and behavioral sciences. as well as from the medically related fields of toxicology. virology. and clinical medicine. • Epidemiologic measures often require counting the number of cases of disease. and race.Quantification • Quantification is a central activity of epidemiology. • Disease distributions are examined according to demographic variables such as age. sex. . .Epidemic • ―The occurrence in a community or region of cases of an illness (or an outbreak) clearly in excess of expectancy…‖ • Relative to usual frequency of the disease. . • First invasion of a communicable disease.Infectious Disease Epidemics • A single case of a long absent communicable disease. • Two cases of such a disease associated in time and place are sufficient evidence of transmission to be considered an epidemic. Concept of Epidemic and NonInfectious Diseases • Some examples that use the concept of an epidemic are: – Love Canal – Brown lung disease – Asbestosis among shipyard workers – Diseases associated with lifestyle . an epidemic on a worldwide scale. .Pandemic • ― . during a pandemic. large numbers of persons may be affected and a disease may cross international borders.‖ An example is a flu pandemic. . . Ascertainment of Epidemics • Surveillance • Epidemic threshold . . • Dissemination of disease-related information. • Analysis and interpretation of these data.Surveillance • The systematic collection of data pertaining to the occurrence of specific diseases. Epidemic Threshold • The minimum number of cases (or deaths) that would support the conclusion than an epidemic was underway. . Historical Antecedents • • • • • • • Environment and disease The Black Death Use of mortality counts Smallpox vaccination Use of natural experiments Identification of specific agents of disease The 1918 influenza pandemic . • He suggested that disease might be associated with the physical environment. and Places in 400 BC. • This represented a movement away from supernatural explanations of disease causation. . Waters.The Environment • Hippocrates wrote On Airs. The Black Death • Occurred between 1346-1352 • Claimed one-quarter to one-third of population of Europe . published Natural and Political Observations Made upon the Bills of Mortality. . in 1662.Use of Mortality Counts • John Graunt. . • Known as the ―Columbus‖ of biostatistics. • Showed excess male over female differences in mortality.John Graunt’s Contributions • Recorded seasonal variations in births and deaths. Edward Jenner • Developed a method for smallpox vaccination . • He investigated a cholera outbreak that occurred during the mid-19th century in Broad Street.Use of Natural Experiments • John Snow was an English physician and anesthesiologist. London. . Golden Square. • Used a spot map of cases and tabulation of fatal attacks and deaths. .Snow’s Contributions • Linked the cholera epidemic to contaminated water supplies. .Snow’s Natural Experiment • Two different water companies supplied water from the Thames River to houses in the same area. • Snow noted that during the next cholera outbreak those served by the Lambeth Company had fewer cases of cholera. • The Lambeth Company moved its source of water to a less polluted portion of the river. .Natural Experiment • Definition: The epidemiologist does not manipulate a risk factor but rather observes the changes in an outcome as the result of a naturally occurring situation. . natural experiments may be the result of legislation.Contemporary Natural Experiments • Currently. policy changes or environmental interventions. Examples of Contemporary Natural Experiments • Seat Belt Law--Did seat belt use reduce fatalities from motor vehicle accidents? • Tobacco Tax--Did the increase in cigarette price decrease the sale of cigarettes? • Helmet Law--Did requiring the use of helmets by motorcyclists reduce the number of head injuries sustained? . • Examined linkage between mortality rates and population density.William Farr • Appointed compiler of abstracts in England. • Provided foundation for classification of diseases (ICD system). . 1839. diseased animal. • Microorganism must be observed in. • Pure culture must. reproduce the disease. and recovered from. when inoculated into a susceptible animal. . • Microorganism must be isolated and grown in pure culture.Koch's Postulates • Microorganism must be observed in every case of the disease. to 40year-olds .1% for other influenza pandemics • Deaths most frequent among 20.The 1918 Influenza Pandemic • Occurred between 1918 and 1919 • Killed 50.5% case-fatality rate versus 0.to 100 million persons worldwide • 2. S. • Wade Hampton Frost was the first professor of epidemiology in the U. . • Joseph Goldberger discovered the cure for pellagra.Other Historical Developments • Alexander Langmuir established CDC’s Epidemic Intelligence Service. • Smoking and lung cancer. breast cancer screening. chemical spills. .Recent Applications of Epidemiology • Framingham Heart Study (since 1948) investigates coronary heart disease risk factors.. Doll and Peto’s study of British doctors’ smoking. e. • AIDS.g. secondhand smoke. Additional Applications of Epidemiology • Infectious diseases – Avian influenza • • • • • Environmental health Chronic diseases Lifestyle and health promotion Psychiatric and social epidemiology Molecular and genetic epidemiology . and Robert Koch .Chapter 1 Quiz • Define the following terms: – Epidemic – Health Phenomena – Morbidity and Mortality – List and describe the 4 Principle Aims of Epidemiology • List the contributions to Epidemiology of: – Hippocrates. Edward Jenner.