Managerial Epidemiology
Helpm31990
51589_PPTx_CH011.pptxChapter 1
The History and Scope of Epidemiology
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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
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2009 H1N1 Influenza
During April 2009, 2 cases of 2009 H1N1 came to the attention of CDC.
The initial cases occurred in the U.S. and then expanded rapidly worldwide.
By summer 2010, the epidemic subsided and an estimated 60 million cases had occurred in the U.S.
Heavily affected people were from 18 to 64 years old. See Exhibit 1-1.
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
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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).
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Definition of Epidemiology
Epidemiology is concerned with the distribution and determinants of health and diseases, morbidity, injuries, disability, and mortality in populations.
Epidemiologic studies are applied to the control of health problems in populations.
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Key Aspects of This Definition
Determinants
Distribution
Population
Health phenomena
Morbidity and mortality
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Determinants
Factors or events that are capable of bringing about a change in health.
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Examples of Determinants
Biologic agents--bacteria
Chemical agents--carcinogens
Less specific factors--stress, drinking, sedentary lifestyle, or high-fat diet
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The Search for Determinants
Outbreak of Fear--Ebola virus in Kikwit, Zaire
Fear on Seventh Ave.--Legionnaires’ disease in New York City
Red Spots on Airline Flight Attendants--dye from life vests
Bioterrorism-Associated Anthrax Cases
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Bioterrorism-Associated Anthrax Cases
Index case reported in Florida
Additional cases, including fatal cases, reported in New York, New Jersey, Connecticut
Contaminated mail linked to some of the cases
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Distribution
Frequency of disease occurrence may vary from one population group to another.
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Disease Distribution Examples
In 2006, death rates from CHD and stroke were higher among African-Americans than among American Indians/Alaskan natives, Asian/Pacific Islanders, or whites.
Coronary heart disease occurrence differs between Hispanics and non-Hispanics.
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Population
Epidemiology examines disease occurrence among population groups, not individuals.
Epidemiology is often referred to as population medicine.
The epidemiologic description indicates variation by age groups, time, geographic location, and other variables.
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Health Phenomena
Epidemiology investigates many different kinds of health outcomes:
Infectious diseases
Chronic diseases
Disability, injury, limitation of activity
Mortality
Active life expectancy
Mental illness, suicide, drug addiction
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Morbidity and Mortality
Morbidity--designates illness.
Mortality--refers to deaths that occur in a population or other group.
Note that most measures of morbidity and mortality are defined for specific types of morbidity or causes of death.
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Aims and Levels
To describe the health status of populations
To explain the etiology of disease
To predict the occurrence of disease
To control the occurrence of disease
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Foundations of Epidemiology
Interdisciplinary
Methods and procedures—quantification
Use of special vocabulary
Epidemic frequency of disease
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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, pathology, virology, genetics, microbiology, and clinical medicine.
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Quantification
Quantification is a central activity of epidemiology.
Epidemiologic measures often require counting the number of cases of disease.
Disease distributions are examined according to demographic variables such as age, sex, race, and other variables, such as exposure category and clinical features.
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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
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Key Terms in “Epidemic”
Communicable disease
An illness caused by an infectious agent that can be transmitted from one person to another.
Infectious disease
A synonym for a communicable disease
Outbreak
A localized disease epidemic, e.g., in a town or health care facility
Concept of Epidemic and Non-Infectious Diseases
Some examples that use the concept of an epidemic are:
Love Canal
Red spots among airline flight attendants
Toxic Shock Syndrome
Brown lung disease
Asbestosis among shipyard workers
Diseases associated with lifestyle
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Pandemic
“ . . . an epidemic on a worldwide scale; during a pandemic, large numbers of persons may be affected and a disease may cross international borders.” An example is a flu pandemic.
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Ascertainment of Epidemics
Surveillance
Epidemic threshold
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Surveillance
The systematic collection of data pertaining to the occurrence of specific diseases.
Analysis and interpretation of these data.
Dissemination of disease-related information
Common activities include monitoring food born disease outbreaks and tracking influenza.
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Epidemic Threshold
The minimum number of cases (or deaths) that would support the conclusion than an epidemic was underway.
This is based on statistical projections.
Figure1-6 demonstrates that the combined pneumonia and influenza deaths peaked substantially above the epidemic threshold during early 2008, late 2009, and early 2011.
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Historical Antecedents
The Cholera Fountain
Environment and disease
The Black Death
Use of mortality counts
Smallpox vaccination
Use of natural experiments
William Farr
Identification of specific agents of disease
The 1918 influenza pandemic
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The Cholera Fountain Dresden, Germany
Dresden, Germany, was spared from a deadly cholera epidemic during 19th Century.
Mid 1800s--Residents constructed a Cholera Fountain to express their gratitude for escaping the cholera epidemic that threatened the city.
The Environment
Hippocrates wrote On Airs, Waters, and Places in 400 BC.
He suggested that disease might be associated with the physical environment.
This represented a movement away from supernatural explanations of disease causation.
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The Black Death
Occurred between 1346-1352.
Claimed one-quarter to one-third of population of Europe.
Use of Mortality Counts
John Graunt, in 1662, published Natural and Political Observations Made upon the Bills of Mortality.
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John Graunt’s Contributions
Recorded seasonal variations in births and deaths
Showed excess male over female differences in mortality
Known as the “Columbus” of biostatistics
See Yearly Mortality Bill for 1632: The 10 Leading Causes of Mortality in Graunt’s Time.
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Edward Jenner
Jenner conducted an experiment to create a smallpox vaccine.
He developed a method for smallpox vaccination.
In 1978 smallpox was finally eliminated worldwide.
Since 1972, routine vaccination of the nonmilitary population of the U.S. has been discontinued.
Use of Natural Experiments
John Snow was an English physician and anesthesiologist.
He investigated a cholera outbreak that occurred during the mid-19th century in Broad Street, Golden Square, London.
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Snow’s Contributions
Linked the cholera epidemic to contaminated water supplies
Used a spot map of cases and tabulation of fatal attacks and deaths
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Snow’s Natural Experiment
Two different water companies supplied water from the Thames River to houses in the same area.
The Lambeth Company moved its source of water to a less polluted portion of the river.
Snow noted that during the next cholera outbreak those served by the Lambeth Company had fewer cases of cholera.
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Natural Experiment
Refers to “naturally occurring circumstances in which subsets of the population have different levels of exposure to a supposed causal factor in a situation resembling an actual experiment, where human subjects would be randomly allocated to groups. The presence of persons in a particular group is typically nonrandom.”
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Ignaz Semmelweis
Mid-19th century, Viennese hospital
Clinical assistant in obstetrics and gynecology
Observed higher mortality rate among the women on the teaching wards for medical students and physicians than on the teaching wards for midwives
Postulated that medical students and physicians had contaminated their hands during autopsies
Introduced the practice of hand washing
William Farr
Appointed compiler of abstracts in England, 1839
Provided foundation for classification of diseases (ICD system)
Used data such as census reports to study occupational mortality in England
Examined linkage between mortality rates and population density
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Koch's Postulates
Microorganism must be observed in every case of the disease
Microorganism must be isolated and grown in pure culture
Pure culture must, when inoculated into a susceptible animal, reproduce the disease
Microorganism must be observed in, and recovered from, diseased animal
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The 1918 Influenza Pandemic
“The Mother of All Pandemics” and Spanish Flu
Occurred between 1918 and 1919
Killed 50- to 100 million persons worldwide
2.5% case-fatality rate versus 0.1% for other influenza pandemics
Deaths most frequent among 20- to 40-year-olds
Other Historical Developments
Alexander Fleming discovered the antimicrobial properties of the mold: led to the discovery of the antibiotic penicillin.
Alexander Langmuir established CDC’s Epidemic Intelligence Service.
Wade Hampton Frost was the first professor of epidemiology in the U.S.
Joseph Goldberger discovered the cure for pellagra.
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Recent Applications of Epidemiology
The Framingham Heart Study (ongoing since 1948) investigates coronary heart disease risk factors.
Smoking and lung cancer; e.g., Doll and Peto’s study of British doctors’ smoking
AIDS, chemical spills, breast cancer screening, second-hand cigarette smoke
Association between HPV and cervical cancer
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Additional Applications of Epidemiology
Infectious diseases
SARS, pandemic influenza 2009 H1N1, Avian influenza
Environmental health
Chronic diseases
Lifestyle and health promotion
Psychological and social epidemiology
Molecular and genetic epidemiology
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