Transcript Document 7133505

Introduction to Public Health and
Epidemiology
HCA 202
Chris Cochran, Ph.D.
August 29, 2005
Brief History of Public Health: GrecoRoman 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
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Brief History of Public Health:
The Middle Ages
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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 13491354 killing one-third of the population
By the end of the middle ages, healthcare
starts to redevelop; rudimentary food-safety
guidelines are introduced
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.
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
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Brief History of Public Health:
The Sanitary Movement
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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
Brief History of Public Health:
The Age of Bacteria
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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
Brief History of Public Health:
Modern Times
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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
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 don’t undo the
advances that we have already made
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What is Health
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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 individual’s
inherent abilities to respond to and to act, and
assuring that all Americans achieve and maintain
a maximum level of functioning. (Healthy People
2010)
Epidemiology Defined for Course
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THE STUDY OF THE DISTRIBUTION AND
DETERMINANTS OF DISEASES AND
INJURIES IN HUMAN POPULATIONS
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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
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
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Objectives of Epidemiology
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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
The Relationship of Epidemiology to
Health Care Managers
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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
Life Expectancy at Birth
Life Expectancy at Birth and at age 65 years 1900, 1950, and 2000
THE EPIDEMIOLOGICAL TRIAD
HOST
VECTOR
AGENT
ENVIRONMENT
Classification for Health Status
Today
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Disease – a state of dysfunction of the normal
physiological processes manifested as signs,
symptoms, and abnormal physical or social function
(includes injury).
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Functional Ability – a process used to represent how
independently an individual can perform or fulfill
expected social roles (physical and mental).
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Quality of Life – multidimensional concepts of
measures covering symptoms/problem complexes,
mobility, physical activity, emotional well-being and
social functioning.
Blum’s Model of Factors Affecting
Health
Health
Environment
Lifestyle
•Fetal
•Attitudes
•Prevention
•Physical
•Behavior
•Cure
•Socio/Cultural
Biology
Medical Care
•Care
•Rehabilitative
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
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Primary Cause of Death 1900
Primary Cause of Death 1997
Source: Healthy People 2010
Descriptive Epidemiology: Person,
Place and Time
 Person
Measures
 Age
 Sex
 Ethnic
group and race
 Social class/social-economic
status
Place Measures
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Place – related by natural barriers or by
political boundaries.
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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
Time and Place
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Time – basic aspect of epidemiology
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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
Using Rates In Epidemiology
Numerator - the number of people/cases
with the disease
 Denominator - (the population at risk)
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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 x:y or
(x/y)k.
 Proportion – Specific type of ratio with
the resultant value expressed as a
percent.
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DEATH RATES
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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.
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Types of Rates
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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.
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Does not represent the risk of dying.
# deaths from a specific disease  Total # deaths in the population X
100 to express as a percent
Other Rates To Consider
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Gender Specific
 Race Specific
 Infant Mortality Rates
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Infant Mortality Rate – Birth to 1 year; Denominator
is live births
 No.
of deaths < 1 year of age/No. of live
births
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Neonatal Mortality Rate
Post-neonatal Mortality Rate
Perinatal Mortality Rate
Years of Productive Life Lost before Age 65 among
Children less than 20 Years
1400
Injuries
1200
Congenital Anomalies
1000
800
Prematurity
600
Sudden Infant Death
Syndrome
Cancer
400
200
Respiratory Disease
0
YPPL in Thousands
Incidence And Prevalence
Knowing Which Is Which
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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.
Uses of Incidence and
Prevalence
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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
Uses of Incidence and
Prevalence
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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
Determining the Case Fatality
Rate
Country
No. of Persons
in Population
1-Year Case Fatality
Rate
Cerebrovascular
Disease (Pct.)
A
250,000
10
B
100,000
25
C
50,000
50
D
250,000
20
Determining the Case Fatality
Rate
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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
4/10,000:n/250,000.
Adjusted Rates
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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.
Formula for Adjusted Rates
 Direct Adjusted
Rates =
 Σ(riNi)/Nt
 Indirect
Adjusted Rates =
 dt/Σ(Rini)](Rt)
Controlling Infectious Disease
Controlling Infectious
Diseases
Epidemic – the occurrence of cases of a
condition in excess of what would be
expected.
 Epidemics in US during 19th Century
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Smallpox
 Cholera
 Yellow Fever
 Typhoid Fever
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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
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Classes of Bacteria and Commonly
Associated Human Diseases
Class
Disease
Staphylococci
Toxic Shock Syndrome
Streptococci
Streptococcal sore throat
Neisseriae
Gonorrhea
Legionellae
Pneumonia
Mycobacteria
Tuberculosis
Spriochetes
Syphilis
Rickettsia
Typhus
Chlamydiae
Urethritis
Characteristics of Infectious Agents
Characterized in terms of biological
classification
 Microbiological agents include:
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Bacteria
 Fungi
 Parasites
 Viruses
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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
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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
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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
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Detection Issues
Reservoirs – can be living (human, animal,
plant) or inanimate (soil, water)
 Clinical cases
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Those who manifest signs and symptoms of the
disease (acute cases)
Those who are infected but don’t show signs or
symptoms (subclinical or inapparent cases)
Carriers - those who serve as the source of
the disease
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)
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Hosting the Agent
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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.
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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