Introduction to Public Health and Epidemiology

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Introduction to Public Health and Epidemiology

• HCA 202
• Chris Cochran, Ph.D.
• August 29, 2005

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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

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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

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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.

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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

• 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

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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

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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

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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

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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)

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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

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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

• 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

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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

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Life Expectancy at Birth
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Life Expectancy at Birth and at age 65 years
1900, 1950, and 2000
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THE EPIDEMIOLOGICAL TRIAD
HOST
VECTOR
AGENT
ENVIRONMENT
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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.

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Blums Model of Factors Affecting Health
Health

• Environment
• Fetal
• Physical
• Socio/Cultural

• Lifestyle
• Attitudes
• Behavior

Biology

• Medical Care
• Prevention
• Cure
• Care
• Rehabilitative

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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
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Primary Cause of Death 1997Source Healthy
People 2010
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Descriptive Epidemiology Person, Place and Time

• Person Measures
• Age
• Sex
• Ethnic group and race
• Social class/social-economic status

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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

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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

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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 xy or (x/y)k.
• Proportion Specific type of ratio with the
  resultant value expressed as a percent.

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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.

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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

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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

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Years of Productive Life Lost before Age 65 among
Children less than 20 Years
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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.

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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

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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

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Determining the Case Fatality Rate
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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.

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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.

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Formula for Adjusted Rates

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

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Controlling Infectious Disease
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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

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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
• Staphylococci
• Streptococci
• Neisseriae
• Legionellae
• Mycobacteria
• Spriochetes
• Rickettsia
• Chlamydiae

• Disease
• Toxic Shock Syndrome
• Streptococcal sore throat
• Gonorrhea
• Pneumonia
• Tuberculosis
• Syphilis
• Typhus
• Urethritis

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Characteristics of Infectious Agents

• Characterized in terms of biological
  classification
• Microbiological agents include
• 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
• 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

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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

• 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