Introduction to Public Health and Epidemiology

HCA 202

Chris Cochran, Ph.D.

August 29, 2005

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

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

Brief History of Public Health: The Middle Ages

Lost knowledge reemergesFirst systematic classification of

diseases undertaken.Occupational related disease is first

identified by Paracelsus. This knowledge is still used today.

Brief History of Public Health: The Renaissance

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

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

Brief History of Public Health:The 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

Brief History of Public Health:Modern 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

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

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 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

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

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

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

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

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

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.

Blum’s Model of Factors Affecting Health

Health

Environment

•Fetal

•Physical

•Socio/Cultural

Lifestyle

•Attitudes

•Behavior

Biology Medical Care

•Prevention

•Cure

•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

Primary Cause of Death 1900

Primary Cause of Death 1997Source: Healthy People 2010

Descriptive Epidemiology: Person, Place and Time

Person MeasuresAgeSexEthnic group and raceSocial class/social-economic

status

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

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

Using Rates In Epidemiology

Numerator - the number of people/cases with the disease

Denominator - (the population at risk)

Basic Descriptive RatesRate - 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.

DEATH RATES

Three essential components of death rates:A population group exposed to the risk of

deathA time periodThe 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.

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

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 < 1 year of age/No. of live births

Neonatal Mortality Rate Post-neonatal Mortality Rate Perinatal Mortality Rate

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

0

200

400

600

800

1000

1200

1400

YPPL in Thousands

Injuries

Congenital Anomalies

Prematurity

Sudden Infant DeathSyndromeCancer

Respiratory Disease

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.

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

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

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

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

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 SmallpoxCholeraYellow FeverTyphoid Fever

How Infectious Diseases Develop

Characteristics of the AgentReservoir of the Agent (where the agent

lives and grows/host)Mode of TransmissionPortal of Entry/ExitSusceptibility of the Host

Classes of Bacteria and Commonly Associated Human Diseases

ClassStaphylococci

Streptococci

Neisseriae

Legionellae

Mycobacteria

Spriochetes

Rickettsia

Chlamydiae

DiseaseToxic Shock Syndrome

Streptococcal sore throat

Gonorrhea

Pneumonia

Tuberculosis

Syphilis

Typhus

Urethritis

Characteristics of Infectious Agents

Characterized in terms of biological classification

Microbiological agents include:BacteriaFungiParasitesViruses

Detection of these agents

Morphological identification in sections of tissue or stains of specimens

Culture isolationUse of Fluorscein-labeled anti-body

stains or immunologic assayDNA/RNA or DNA-DNA hybridizationAntibody or cell-meditated immune

responses

Components of accurately identifying infectious diseases

The specimenAdequacy of material being testedSelection of appropriate body area for

testingMethod of CollectionTransport of the Specimen to the Lab

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

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 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)

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