History of Epidemiology

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History 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.)

• 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 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 EPIDEMIOLOGY
3. STATISTICS ----- Emphasis on the scientific
method, quantification and measurement, and
hypothesis testing. In 1960s, many epidemiologis
ts were statisticians.
4. SOCIAL SCIENCES ----- Investigation of human
behavior in relation to disease, and methods
of data collection (surveys, etc.)
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ROOTS OF MODERN EPIDEMIOLOGY
5. COMPUTER SCIENCES ----- Emergence of chronic
disease epidemiology required the ability
to handle large amounts of data and to perform
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 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 Evidence,
and Attendant Concerns
Epidemiology provides varying levels of
information
REQUIREMENTS
INFERENCE
Relations between operational measurements among
study measurements
None
Accurate measurement of both exposure and disease
Association between measured exposure and disease
among study participants
Freedom from confounding
Causal effect of exposure on disease in the
study population
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Levels of Inference from Epidemiologic Evidence,
and Attendant Concerns
Epidemiology provides varying levels of
information
REQUIREMENTS
INFERENCE
Causal effect of exposure on disease in external
populations
Generalizability (external validity)
Amenability of exposure to modification
Prevention of disease through elimination or
reduction of exposure
Substantial public health impact from elimination
or reduction of exposure
Large attributable fraction
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EVOLVING FIELD OF EPIDEMIOLOGY
Chief Causes of Death in the U.S. -- 1900

• 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

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Chief Causes of Death in the U.S. -- 2001

• Disease of heart 248
• Malignant neoplasms 196
• Cerebrovascular diseases 58
• Chronic lower respiratory diseases 44
• Unintentional injuries 36
• Diabetes mellitus 25
• Pneumonia influenza 22

Age-adjusted per 100,000
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Leading Causes of Death in Children In Developing
Countries -- 2002

• 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

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Causes of Mortality Worldwide 2002 Ages 15 -
59
Cause Deaths (000) HIV/AIDS 2279 Ischemi
c heart disease 1332 Tuberculosis 1036 Road
traffic injuries 814 Cerebrovascular
disease 783 Self-inflicted injuries 672 Viole
nce 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 Trac
hea, 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 Unipola
r depressive disorders 57843 Tuberculosis 283
80 Road traffic injuries 27264 Ischemic heart
disease 26155 Alcohol use disorders 19567 Hear
ing 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 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 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 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 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 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

• 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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ETHICS

• 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 individuals health information is
  properly protected, while allowing the flow of
  health information needed to promote high-quality
  health care and to protect the publics health
  and well-being.

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HIPAA

• 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 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 4
What are the important criteria that IRBs
consider in approving human research studies?
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Discussion Question 4

• Criteria include
• Risks to study participants are minimized.
• Risks are reasonable in relation to anticipated
  benefits.
• Selection of study participants is equitable.
• Informed consent is obtained and documented for
  each participant.
• Adequate monitoring of data collection to ensure
  the safety of study participants.
• Privacy of participants and confidentiality of
  data are protected.

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THE HOST - ENVIRONMENT INTERACTION
ANKYLOSING SPONDYLITIS

• 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)

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THE HOST - ENVIRONMENT INTERACTION
Virtually all chronic diseases have
multi-factorial etiologies -- 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 disease
Usual time of diagnosis
Onset of symptoms
Exposure
Pathologic changes
Stage of recovery, disability or death
Stage of subclinical disease
Stage of clinical disease
Stage of susceptibility
PRIMARY PREVENTION
SECONDARY PREVENTION
TERTIARY PREVENTION
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The 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 disease
(contd)

• 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 disease
(contd)

• 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 disease
(contd)

• 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 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 PREVENTION (contd)

• 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 PREVENTION (contd)

• LEVEL Tertiary
• DESCRIPTION Rehabilitation and
  prevention of further disease or disability
• EXAMPLE Oxygen therapy facilitating
  ambulation with technical devices

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PREVENTION 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 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)PRIMARY PREVENTION

• Prevention of disease by controlling risk factors
  (e.g., non-smoking promotion)

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LEVELS OF PREVENTION (Review)SECONDARY
PREVENTION

• Reduction in consequences of disease by early
  diagnosis and treatment
• (e.g., cervical cancer screening)

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LEVELS OF PREVENTION (Review)TERTIARY
PREVENTION

• Reduction in complications of disease
• (e.g., MV crashes and ICU)