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History of EpidemiologyHistory of Epidemiology
HIPPOCRATES (400 BC): “On Airs, Waters, and Places” –Hypothesized that disease might be associated with the physical environment, including seasonal variation in illness.
JOHN GRAUNT (1662): “Nature and Political Observations Made Upon the Bills of Mortality” – First to employ quantitative methods in describing population vital statistics.
JOHN SNOW (1850): Formulated natural epidemiological experiment to test the hypothesis that cholera was transmitted by contaminated water.
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History of Epidemiology (cont.)History of Epidemiology (cont.)
DOLL & HILL (1950): Used a case-control design to describe and test the association between smoking and lung cancer.
FRANCES at al. (1950): Huge formal field trial of the Poliomyelitis vaccine in school children.
DAWBER et al. (1955): Used the cohort design to study risk factors for cardiovascular disease in the Framingham Heart Study.
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ROOTS OF MODERN EPIDEMIOLOGYROOTS OF MODERN EPIDEMIOLOGY
1. ACUTE DISEASE INVESTIGATION----- Emphasis on empirical systematic
investigation, biology, and environment/host manipulation
2. MEDICINE----- All early epidemiologists were
physicians.
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ROOTS OF MODERN EPIDEMIOLOGYROOTS OF MODERN EPIDEMIOLOGY
3. STATISTICS----- Emphasis on the scientific method,
quantification and measurement,and hypothesis testing. In 1960s, manyepidemiologists were statisticians.
4. SOCIAL SCIENCES----- Investigation of human behavior in
relation to disease, and methods ofdata collection (surveys, etc.)
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ROOTS OF MODERN EPIDEMIOLOGYROOTS OF MODERN EPIDEMIOLOGY
5. COMPUTER SCIENCES----- Emergence of “chronic” disease
epidemiology required the ability tohandle large amounts of data and toperform complex analyses.
6. MANAGERIAL SCIENCES----- Management principles for acquisition
of grants, research collaboration, and management of clinical trials.
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ROOTS OF MODERN EPIDEMIOLOGYROOTS OF MODERN EPIDEMIOLOGY
7. GENOMICS----- 2001 marked first publication of draft sequences of the human genome. Intensive investigations being conducted to identify “disease susceptibility genes” “gene-environment” interactions, and “gene-gene” interactions.
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Levels of Inference from Epidemiologic Levels of Inference from Epidemiologic Evidence, and Attendant ConcernsEvidence, and Attendant Concerns
Epidemiology provides varying levels of information:
Freedom from “confounding”
Causal effect of exposure on disease in the study population
Accurate measurement of both exposure and disease
Association between measured exposure and disease among study participants
NoneRelations between operational measurements among study measurements
REQUIREMENTSINFERENCE
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Levels of Inference from Epidemiologic Levels of Inference from Epidemiologic Evidence, and Attendant ConcernsEvidence, and Attendant Concerns
Epidemiology provides varying levels of information:
Large “attributable fraction”
Substantial public health impact from elimination or reduction of exposure
Amenability of exposure to modification
Prevention of disease through elimination or reduction of exposure
Generalizability (external validity)
Causal effect of exposure on disease in external populations
REQUIREMENTSINFERENCE
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EVOLVING FIELD OF EPIDEMIOLOGYEVOLVING FIELD OF EPIDEMIOLOGY
Pneumonia/Influenza 11.8% Tuberculosis 11.3% Gastritis, enteritis, colitis 8.3% Heart disease 8.0% Senility, ill-defined conditions 6.8% Vascular lesions affecting CNS 6.2% Nephritis and renal sclerosis 4.7%
Chief Causes of Death in the U.S. -- 1900
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Disease of heart248
Malignant neoplasms196
Cerebrovascular diseases 58 Chronic lower respiratory diseases 44 Unintentional injuries 36 Diabetes mellitus 25 Pneumonia & influenza 22
Chief Causes of Death in the U.S. -- 2001*
*Age-adjusted per 100,000
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Cause of Death % of all Deaths
Perinatal conditions 23.1 Lower respiratory infections 18.1 Diarrhoeal diseases 15.2 Malaria 10.7 Measles 5.4 Congenital anomalies 3.8 HIV/AIDS 3.6 Pertussis 2.9 Other 17.2
Leading Causes of Death in ChildrenIn Developing Countries -- 2002
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Causes of Mortality Worldwide: 2002: Ages 15 - 59
Cause Deaths (000)
HIV/AIDS 2279
Ischemic heart disease 1332
Tuberculosis 1036
Road traffic injuries 814
Cerebrovascular disease 783
Self-inflicted injuries 672
Violence 473
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Causes of Mortality Worldwide: 2002: Ages 60 and Older
Cause Deaths (000)
Ischemic heart disease 5825
Cerebrovascular disease 4689
COPD 2399
Lower respiratory infections 1396
Trachea, bronchus, lung cancers 928
Diabetes mellitus 754
Hypertensive heart disease 735
Stomach cancer 605
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Causes of Disease Burden (DALYs) Worldwide: 2002: Ages 15 - 59
Cause DALYs (000)
HIV/AIDS 68661
Unipolar depressive disorders 57843
Tuberculosis 28380
Road traffic injuries 27264
Ischemic heart disease 26155
Alcohol use disorders 19567
Hearing loss, adult onset 19486
Violence 18962
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Causes of Disease Burden (DALYs) Worldwide: 2002: Ages 60 and Older
Cause DALYs (000)
Ischemic heart disease 31481
Cerebrovascular disease 29595
COPD 14380
Alzheimers and other dementias 8569
Cataracts 7384
Lower respiratory infections 6597
Hearing loss, adult onset 6548
Trachea, bronchus, lung cancers 5952
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EVOLVING FIELD OF EPIDEMIOLOGYEVOLVING FIELD OF EPIDEMIOLOGY
Historically, in developed countries, there has been a marked shift in the leading causes of mortality from “infectious” to “chronic” diseases.
In the U.S. today, the fastest growing segment of the population is aged 85 and older.
Virtually all “chronic” diseases have multi-factorial etiologies.
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Discussion Question 3Discussion Question 3
If a “cure” was found for heart
disease, how might this likely affect
mortality rates from: (1) AIDS; and
(2) Cancer in the United States?
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Discussion Question 3Discussion Question 3
Most likely:
1. AIDS-related mortality would be largely unaffected since most deaths from AIDS occur in persons not at high risk (age) for heart disease mortality.
2. Cancer mortality would increase since persons who would have died from heart disease would now be at risk of dying from cancer.
This concept of one cause of mortality affecting another is know as “competing risks.”
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PRACTICAL AND ETHICAL ISSUESPRACTICAL AND ETHICAL ISSUES
Measures of disease and exposure occurrence are often not easy to obtain.
Many diseases occur infrequently in human populations.
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PRACTICAL AND ETHICAL ISSUESPRACTICAL AND ETHICAL ISSUES
Unlike experimental science, the investigator cannot manipulate study variables (i.e those hypothesized to be causes of disease).
Investigator must deal with budgetary and subject privacy concerns.
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EXAMPLES OF UNETHICAL “RESEARCH”EXAMPLES OF UNETHICAL “RESEARCH” Criminal and unscientific behavior of physicians in
concentration camps in Nazi Germany – led to adoption of Nuremberg Code (1947).
1936 – U.S. Public Health Service started study of effects of untreated syphilis in Tuskegee, AL long after effective treatment for the disease was known.
1963- Jewish Chronic Diseases Hospital – 22 elderly patients injected with cancer cells without their knowledge to test immunological response.
Willowbrook State Hospital, NY: retarded children deliberately infected with viral hepatitis to study natural history.
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ETHICSETHICS 1974: Congress established the National
Commission for the Protection of Human Subjects of Biomedical and Behavioral Research.
Requires the establishment of Institutional Review Boards (IRBs) for all research funded in whole or in part by the federal government.
1996: Health Insurance Portability and Accountability Act (HIPAA): Privacy Rule issued to assure that individual’s health information is properly protected, while allowing the flow of health information needed to promote high-quality health care and to protect the public’s health and well-being.
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HIPAAHIPAA
The HIPAA Privacy Rule protects individual “identifiable” health information known as “protected health information” transmitted or maintained in any form or medium. Includes:
--- Demographic or other information relating to past, current, or future physical or mental health or condition of an individual
--- Provision or payment of health care to an individual that is created or received by a health care provider, health plan, employer, or health care clearinghouse
--- Individual genetic information
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SOME PROFESSIONAL AND ETHICAL ISSUESSOME PROFESSIONAL AND ETHICAL ISSUES
Should informed consent be required for routine review of medical records?
Who should have access to the study data, and when?
How should study findings be disseminated to the public?
Should epidemiologists be advocates for specific public health policies?
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Discussion Question 4Discussion Question 4
What are the important criteria that
IRBs consider in approving human
research studies?
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Discussion Question 4Discussion Question 4
Criteria include:
1. Risks to study participants are minimized.2. Risks are reasonable in relation to anticipated
benefits.3. Selection of study participants is equitable.4. Informed consent is obtained and
documented for each participant.5. Adequate monitoring of data collection to
ensure the safety of study participants.6. Privacy of participants and confidentiality of
data are protected.
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THE HOST - ENVIRONMENT INTERACTIONTHE HOST - ENVIRONMENT INTERACTION
Persons with HLA-B27 approximately 90 times more likely to develop the disease (Genetic Susceptibility)
However, only 10% of the individuals with HLA-B27 will develop the disease (Environmental Exposure)
ANKYLOSING SPONDYLITIS
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THE HOST - ENVIRONMENT INTERACTIONTHE HOST - ENVIRONMENT INTERACTION
“Virtually all chronic diseases have multi-factorialetiologies” -- many may have infectious components.
Enteroviruses Type I diabetes
Epstein Barr virus B-cell lymphomas
Chlamydia pneumoniae Heart disease
Helicobacter pylori Peptic ulcers
Hepatitis B and C Liver cancer
Borna disease virus Schizophrenia
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Natural history of diseaseNatural history of disease
Stage ofsusceptibility
Stage of subclinical
disease
Stage of clinical disease
Stage of recovery,
disability or death
PRIMARY PRIMARY PREVENTIONPREVENTION SECONDARY SECONDARY
PREVENTIONPREVENTION TERTIARY TERTIARY PREVENTIONPREVENTION
Exposure
Pathologicchanges
Onset of symptoms
Usual time of diagnosis
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The natural history of diseaseThe natural history of disease
STAGE 1: Susceptibility
DESCRIPTION: Risk factors which assist the development of
disease exist, but disease has not developed
EXAMPLE: Smoking
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The natural history of diseaseThe natural history of disease (cont’d) (cont’d)
STAGE 2: Presymptomatic disease
DESCRIPTION: Changes have occurred to lead toward illness but disease is not yet
clinically detectable
EXAMPLE: Alveoli deteriorate
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The natural history of diseaseThe natural history of disease (cont’d) (cont’d)
STAGE 3: Clinical Disease
DESCRIPTION: Detectable signs and/or symptoms of disease exist
EXAMPLE: Emphysema detected by pulmonary function test
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The natural history of diseaseThe natural history of disease (cont’d) (cont’d)
STAGE 4: Disability
DESCRIPTION: Disease has progressed to the point of causing a
residual effect
EXAMPLE: Person has difficulty breathing
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LEVELS OF PREVENTIONLEVELS OF PREVENTION
LEVEL: Primary
DESCRIPTION: Promote general health
and avoid risk factors for
disease --- Utilize protective measures to prevent
susceptibility and presymptomatic disease
EXAMPLE: Stop smoking or choose not to start; avoid areas
where people are smoking
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LEVELS OF PREVENTIONLEVELS OF PREVENTION (cont’d) (cont’d)
LEVEL: Secondary
DESCRIPTION: Early detection and timely treatment
EXAMPLE: Routine pulmonary function tests for those at risk; medicine to help
patients breath more easily; smoking cessation
programs if patient smokes
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LEVELS OF PREVENTIONLEVELS OF PREVENTION (cont’d) (cont’d)
LEVEL: Tertiary
DESCRIPTION: Rehabilitation and prevention of further
disease or disability
EXAMPLE: Oxygen therapy; facilitating ambulation with technical devices
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PREVENTION APPROACHESPREVENTION APPROACHES
Population-Based Approach:• Preventive measure widely applied to
an entire population (public health approach)
• Strive for small absolute change among many persons
• Must be relatively inexpensive and non-invasive
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PREVENTION APPROACHESPREVENTION APPROACHES
High-Risk Approach:
• Target group of individual at high risk
• Strive for strong risk factor control
• Often times requires clinical action to identify the high risk group and to motivate risk factor control.
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LEVELS OF PREVENTION (Review)LEVELS OF PREVENTION (Review)
PRIMARY PREVENTIONPRIMARY PREVENTIONPrevention of disease by
controlling risk factors (e.g.,
non-smoking promotion)
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Reduction in consequences of disease
by early diagnosis and treatment
(e.g., cervical cancer screening)
LEVELS OF PREVENTION (Review)LEVELS OF PREVENTION (Review)
SECONDARY PREVENTIONSECONDARY PREVENTION
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Reduction in complications of disease
(e.g., MV crashes and ICU)
LEVELS OF PREVENTION (Review)LEVELS OF PREVENTION (Review)
TERTIARY PREVENTIONTERTIARY PREVENTION