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Introduction to Public Health and Epidemiology

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Title: Introduction to Public Health and Epidemiology


1
Introduction to Public Health and Epidemiology
  • HCA 202
  • Chris Cochran, Ph.D.
  • August 29, 2005

2
Brief History of Public Health Greco-Roman Period
  • Hippocrates Whoever wishes to pursue properly
    the science of medicine ought to consider the
    effects of the season of the year, the hot winds
    and the cold, the properties of the waters, the
    setting of the town, the behavior of the people
  • Romans build aqueducts to bring water from
    distant sources and to remove sewage

3
Brief History of Public Health The Middle Ages
  • Public health declines
  • Disease and lack of sanitation rampant
  • Increase in trade between cities also enabled the
    spread of disease
  • Bubonic plague hits Europe between 1349-1354
    killing one-third of the population
  • By the end of the middle ages, healthcare starts
    to redevelop rudimentary food-safety guidelines
    are introduced

4
Brief History of Public Health The Renaissance
  • Lost knowledge reemerges
  • First systematic classification of diseases
    undertaken.
  • Occupational related disease is first identified
    by Paracelsus. This knowledge is still used today.

5
History of Public Health The Enlightenment
  • First surveys seeking information related to
    diseases and health are developed
  • Edward Jenner observed that milkmaids who had
    cowpox did not contract smallpox
  • Industrial revolution improves sanitation but
    creates new environmental hazards of water and
    air

6
Brief History of Public Health The Sanitary
Movement
  • Regular bathing, clean water and controlled waste
    disposal is promoted
  • To control fires, New York constructs one of the
    first municipal water systems
  • River and Harbor Act of 1899, implemented by
    federal government to protect waterways from
    dumping of debris becomes the basis for
    protection from pollutants
  • Pasteur and Koch develop germ theory of disease
  • John Snow initiates the study of Epidemiology
  • Science and engineering expands at rapid pace
    furthering the advance of medicine
  • Use of antiseptics in hospitals allows them to
    become places where the sick can be treated, not
    places to die

7
Brief History of Public HealthThe Age of
Bacteria
  • Connection made between bacteria and viruses and
    disease
  • Pasteurization U.S. adopts the Pure Food and Drug
    Act
  • Important species of bacteria are isolated and
    identified including Escherichia coli and
    staphylococcus
  • Identification of vectors helps battle
    communicable disease.
  • Elements of the immune system are identified
    creating regional laboratories devoted to disease
    research
  • Drinking water and sewage treatment plants causes
    a decline in typhoid

8
Brief History of Public HealthModern Times
  • WWI introduced poison gas as warfare
  • Draining of swamps reduces mosquito borne disease
  • In 1919, Spanish Flu pandemic killed 30 million
    world-wide
  • Fleming discovers penicillin in 1928
  • In WWII, protecting soldiers from disease leads
    to more death from injuries and wounds than from
    infection for the first time in history of wars
  • The World Health Organization was formed in 1948
  • Salk invents the polio vaccine
  • In 1978, smallpox is eradicated from the planet
  • In 1979, the first cases of AIDS appear
  • In 1980s, poison gas once again used in warfare
    (Iran-Iraq war)
  • New diseases emerge AIDS, SARS, drug-resistant
    staphylococcus

9
Public Health Priorities for the Future
  • Continue the pursuit of the eradication of
    disease and its causes
  • Getting the public to understand that preventing
    disease does not rely solely on new medicine or
    inventions
  • Making sure that we dont undo the advances that
    we have already made

10
What is Health
  • A state of complete physical, mental and social
    well-being, not merely the absence of disease or
    infirmity (WHO).
  • Preventing premature death and preventing
    disability, preserving a physical environment
    that supports human life, cultivating family and
    community support, enhancing each individuals
    inherent abilities to respond to and to act, and
    assuring that all Americans achieve and maintain
    a maximum level of functioning. (Healthy People
    2010)

11
Epidemiology Defined for Course
  • THE STUDY OF THE DISTRIBUTION AND DETERMINANTS OF
    DISEASES AND INJURIES IN HUMAN POPULATIONS
  • Concerned with frequencies and types of illnesses
    and injuries in groups of people factors that
    influence their distribution
  • Implies that disease is not randomly distributed
  • Speculates that a chain of events must occur for
    illness or disability to take place

12
Epidemiology
  • Endemic habitual presence of a disease for a
    population within a given geographic area
    expectations
  • Epidemic occurrence of a group of illnesses
    within a given geographic area in excess of
    normal expectations
  • Pandemic world-wide or broad epidemic beyond
    many geographic regions

13
Objectives of Epidemiology
  • Identify the etiology or cause of disease and
    risk factors
  • Determine the extent of the disease in the
    community
  • To study the natural history and prognosis of the
    disease
  • To evaluate existing and new preventive measures
    and therapeutic measures and modes for health
    care delivery
  • To help make public policy

14
The Relationship of Epidemiology to Health Care
Managers
  • Understanding the increase/decrease in size of
    service populations
  • To understand the characteristics and health
    status of the population for planning purposes
  • To understand the consequences of health care
    problems
  • To mesh the service organizations to the needs of
    the population
  • To monitor performance by the organizations
  • To modify the structure and processes and respond
    to environmental change
  • To better formulate and evaluate public policy

15
Life Expectancy at Birth
16
Life Expectancy at Birth and at age 65 years
1900, 1950, and 2000
17
THE EPIDEMIOLOGICAL TRIAD
HOST
VECTOR
AGENT
ENVIRONMENT
18
Classification for Health Status Today
  • Disease a state of dysfunction of the normal
    physiological processes manifested as signs,
    symptoms, and abnormal physical or social
    function (includes injury).
  • Functional Ability a process used to represent
    how independently an individual can perform or
    fulfill expected social roles (physical and
    mental).
  • Quality of Life multidimensional concepts of
    measures covering symptoms/problem complexes,
    mobility, physical activity, emotional well-being
    and social functioning.

19
Blums Model of Factors Affecting Health
Health
  • Environment
  • Fetal
  • Physical
  • Socio/Cultural
  • Lifestyle
  • Attitudes
  • Behavior

Biology
  • Medical Care
  • Prevention
  • Cure
  • Care
  • Rehabilitative

20
Prevention and Health Promotion
  • Primary inhibition of the development of the
    disease before it occurs
  • Secondary early detection and treatment of a
    disease
  • Tertiary the rehabilitation or restoration of
    effective functioning

21
Primary Cause of Death 1900
22
Primary Cause of Death 1997Source Healthy
People 2010
23
Descriptive Epidemiology Person, Place and Time
  • Person Measures
  • Age
  • Sex
  • Ethnic group and race
  • Social class/social-economic status

24
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25
Place Measures
  • Place related by natural barriers or by
    political boundaries.
  • Natural boundaries characterized by particular
    environmental or climatic condition (temperature,
    humidity, rainfall, altitude, mineral content,
    etc.).
  • Place diseases parasitic diseases that may be
    due to certain factors such as tropics,
    temperate, or other conditions.
  • Political subdivisions vary from entire nations
    to counties, cities, towns, and boroughs

26
Time and Place
  • Time basic aspect of epidemiology
  • Secular trends (long-term variations, which occur
    over periods of time including years and
    decades). Good for studying "birth cohorts".
  • Cyclic change recurrent alteration in the
    frequency of disease (seasonal changes, for
    example influenza)
  • Clusters in time and place difficult to
    determine the significance of linkages because
    there is no defined denominator

27
Using Rates In Epidemiology
  • Numerator - the number of people/cases with the
    disease
  • Denominator - (the population at risk)

28
Basic Descriptive Rates
  • Rate - Number of events, cases, or deaths in a
    time period/Population in same area
  • Ratio Expresses the relationship between 2
    numbers in the form of xy or (x/y)k.
  • Proportion Specific type of ratio with the
    resultant value expressed as a percent.

29
DEATH RATES
  • Three essential components of death rates
  • A population group exposed to the risk of death
  • A time period
  • The number of deaths occurring in the population
    during that time period (NOTE best to take the
    population for the mid-point of the period being
    studied.

30
Types of Rates
  • Crude Death Rate Total deaths from all causes
    during a 12 month period ? Total persons in the
    population at the midpoint of the period
  • Cause specific death rates deaths from a
    specific disease ? persons in the population at
    the midpoint of the period
  • Age specific death rates deaths in a specific
    age group ? persons in that age group Usually
    X 100,000
  • Case fatality rate Represents the risk of dying
    over a specified period of time for people with a
    certain disease
  • Proportionate mortality ratio Represents the
    proportion of total deaths that are due to a
    specific cause.
  • Does not represent the risk of dying.
  • deaths from a specific disease ? Total deaths
    in the population X 100 to express as a percent

31
Other Rates To Consider
  • Gender Specific
  • Race Specific
  • Infant Mortality Rates
  • Infant Mortality Rate Birth to 1 year
    Denominator is live births
  • No. of deaths lt 1 year of age/No. of live births
  • Neonatal Mortality Rate
  • Post-neonatal Mortality Rate
  • Perinatal Mortality Rate

32
Years of Productive Life Lost before Age 65 among
Children less than 20 Years
33
Incidence And PrevalenceKnowing Which Is Which
  • Incidence measures the number of new cases in an
    at-risk population
  • Prevalence measures the number of existing cases
    in an at-risk population
  • Point Prevalence - the number of existing cases
    of a disease at a specific period of time. This
    includes new cases (Incidence).
  • Period Prevalence - refers to the number of cases
    during a period or interval. This can include new
    and recurring cases.

34
Uses of Incidence and Prevalence
  • Prevalence is useful as planning tool
  • Can be used to express burden of some attribute
    in the population
  • Can monitor control programs for chronic illness
  • Point prevalence can track illness over time
  • Incidence rates are fundamental tools for
    etiologic studies of acute and chronic illness

35
Uses of Incidence and Prevalence
  • Comparing incidence between groups is useful for
    measuring affects of risk between populations
  • High prevalence does not signify risk, it may
    merely reflect a change in survival rate
  • Low prevalence may reflect a rapidly fatal
    disease (or easily curable)
  • Prevalence favors inclusion of chronic illness
    over acute illness

36
Determining the Case Fatality Rate
37
Determining the Case Fatality Rate
  • To determine which country has the largest annual
    number of new cases - obtain the rate of cases
    per 10,000 and compare it to the total
    population.
  • For example, country A has 4 cases per 10,000 and
    a total population of 250,000. For every 10,000
    population there are 4 cases. Therefore, the
    number of new cases would be 4/10,000n/250,000.

38
Adjusted Rates
  • Adjusted rates or standardized rates help remove
    the effects of differences in composition of
    various populations (for example, age
    differences).
  • Direct Adjusted Rates - age specific rates
    observed in 2 or more study populations are
    applied to an arbitrarily chosen standard
    population.
  • Indirect rate adjustment - compares 2 or more
    populations in which the age-specific rates are
    not known or are excessively variable because of
    the small size of the population. In this case,
    the rates of the more stable population are
    applied to the population of the smaller group.

39
Formula for Adjusted Rates
  • Direct Adjusted Rates
  • S(riNi)/Nt
  • Indirect Adjusted Rates
  • dt/S(Rini)(Rt)

40
Controlling Infectious Disease
41
Controlling Infectious Diseases
  • Epidemic the occurrence of cases of a condition
    in excess of what would be expected.
  • Epidemics in US during 19th Century
  • Smallpox
  • Cholera
  • Yellow Fever
  • Typhoid Fever

42
How Infectious Diseases Develop
  • Characteristics of the Agent
  • Reservoir of the Agent (where the agent lives and
    grows/host)
  • Mode of Transmission
  • Portal of Entry/Exit
  • Susceptibility of the Host

43
Classes of Bacteria and Commonly Associated Human
Diseases
  • Class
  • Staphylococci
  • Streptococci
  • Neisseriae
  • Legionellae
  • Mycobacteria
  • Spriochetes
  • Rickettsia
  • Chlamydiae
  • Disease
  • Toxic Shock Syndrome
  • Streptococcal sore throat
  • Gonorrhea
  • Pneumonia
  • Tuberculosis
  • Syphilis
  • Typhus
  • Urethritis

44
Characteristics of Infectious Agents
  • Characterized in terms of biological
    classification
  • Microbiological agents include
  • Bacteria
  • Fungi
  • Parasites
  • Viruses

45
Detection of these agents
  • Morphological identification in sections of
    tissue or stains of specimens
  • Culture isolation
  • Use of Fluorscein-labeled anti-body stains or
    immunologic assay
  • DNA/RNA or DNA-DNA hybridization
  • Antibody or cell-meditated immune responses

46
Components of accurately identifying infectious
diseases
  • The specimen
  • Adequacy of material being tested
  • Selection of appropriate body area for testing
  • Method of Collection
  • Transport of the Specimen to the Lab

47
Detection Issues
  • Pathogeneity the ability of an organism to
    alter normal cellular and physiological processes
  • Virulence the ability of the organism to
    produce over infection
  • Incubation Period the time from point of
    infection to onset of disease

48
Detection Issues
  • Reservoirs can be living (human, animal, plant)
    or inanimate (soil, water)
  • Clinical cases
  • Those who manifest signs and symptoms of the
    disease (acute cases)
  • Those who are infected but dont show signs or
    symptoms (subclinical or inapparent cases)
  • Carriers - those who serve as the source of the
    disease

49
Mode of Transmission
  • Direct transmission - actual contact with an
    infected host
  • Indirect transmission - contact with a
    contaminated object (contaminated needles,
    receptacles, etc.)
  • Droplet spread - such as sneezing or coughing
    (inhalation)

50
Hosting the Agent
  • Portal of Exit - where the organism leaves the
    body
  • Portal of Entry - where the organism enters the
    body
  • Host Susceptibility - depends on genetic factors,
    general health, and immunity. This usually refers
    to the condition of the host and the level of
    resistance.
  • Passive natural immunity - passed from the mother
    to the fetus
  • Passive Artificial Immunity - inoculation of
    specific protective antibodies
  • Active Immunity can be natural (previous exposure
    to disease or previous exposure to preventative
    measures)
  • To develop disease, individual must be
    susceptible and exposed
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