Download Epidemiology - Health Science

Chapter 1
Foundations of
Epidemiology
What Is Health?
 The absence of illness
 Six dimensions of health
What Are the Six Dimensions of
Health?
Physical
Ability of the human body to function properly; includes physical fitness and activities of
daily living.
Social
Ability to have satisfying relationships; interaction with social institutions and societal
mores.
Mental
Ability to think clearly, reason objectively, and act properly.
Emotional
Ability to cope, adjust and adapt; self-efficacy and self-esteem.
Spiritual
Feeling as if part of a greater spectrum of existence; personal beliefs and choices.
Environmental Comprised of external factors (i.e., one’s surroundings such as habitat or occupation) and
internal factors (i.e., one’s internal structure such as genetics).
What Is Public Health?
 Public health is the science and art of promoting
health and extending life on the population
level.
 Public health is concerned with threats to health
in the population (a group of people sharing one
or more characteristics).
 The mission of public health is to ensure
conditions that promote the six dimensions of
health in the population as a whole.
What Is the Meaning of
Population?
 Population refers to a collection of individuals
that share one or more observable personal or
observational characteristic from which data may
be collected and evaluated.
 Social
 Economic
 Family (marriage and divorce)
 Work and labor force
 Geographic factors
How Does Public Health Relate to
Epidemiology?
 There are many subfields of public health,
including epidemiology, biostatistics, and health
services.
 Because of its central role in public health,
epidemiology is commonly referred to as the
foundation of public health.
What Is Epidemiology?
 Epidemiology is the study of the distribution
and determinants of health-related states or
events in human populations, and the
application of this study to prevent and control
health problems.
What Is Epidemiology?
 The word epidemiology is based on the Greek
words:
 epi – prefix meaning on, upon, or befall
 demos – root meaning the people
 logos – suffix meaning the study
 In other words, epidemiology is the study of what
befalls the population.
Key Terms in the Definition
 Study – Epidemiology involves sound methods of
scientific investigation
 Methods rely on careful observation and the use of
valid comparison groups to determine whether the
observed health events differ from what might be
expected.
Key Terms in the Definition
 Distribution
 Study of frequency and pattern of health events in the
population
 Frequency – number, and number in relation to the
population
 Pattern – the health-related state or event by person,
place, and time characteristics
Key Terms in the Definition
 Determinants
 Search for causes and other factors of health-related
states or events
Key Terms in the Definition
 Health-related states or events
 Disease states

cholera, influenza, pneumonia, mental illness
 Conditions associated with health

physical activity, nutrition, environmental poisoning,
seat belt use, and provision and use of health
services
 Events

injury, drug abuse, and suicide
Key Terms in the Definition
 Application of this study to prevent and control
health problems
Why is epidemiology considered by
many to be the foundation of public
health?
 Because of its central role in carrying out the three
core public health functions:
1.The assessment and monitoring of the health of
communities and populations at risk to identify health
problems and priorities.
2.The formulation of public policies designed to solve
identified local and national health problems and priorities.
3.To assure that all populations have access to appropriate
and cost-effective care, including health promotion and
disease prevention services, and evaluation of the
effectiveness of that care.
The Epidemiologic Focus
 Clinical focus vs. epidemiologic focus
 Clinical focus treats the patient as an individual
 Epidemiologic focus provides information that helps
determine public health action to prevent and control
health problems
Epidemiology and the Scientific
Method
 Epidemiology uses the scientific method to
describe and analyze health-related states or
events.
What Is the Scientific Method?
 The scientific method involves using appropriate
study designs and statistical techniques for
investigating an observable occurrence and
acquiring new knowledge.
 The health problem
 Hypotheses
 Statistical testing
 Interpretation
 Dissemination
Study Designs in Epidemiology
 Descriptive epidemiology
 Involves study designs used to answer Who?,
What?, When?, and Where?
 Analytic epidemiology
 Involves study designs used to answer Why? and
How?
 Later chapters will focus on describing these
study designs.
The Importance of Descriptive
Epidemiology
 A means to characterizing the distribution of
health-related states or events by
 Person – who?
 Place – where?
 Time – when?
 Clinical criteria – what?
The Importance of Analytic
Epidemiology
 A means to identifying and quantifying
associations, testing hypotheses, and supporting
statements about causality
 Explains why and how health-related states or
events occur
Selected Activities Performed in
Epidemiology
 Identifying risk factors for disease, injury, and
death
 Describing the natural history of disease
 Identifying individuals and populations at
greatest risk for disease
 Identifying where the public health problem is
greatest
 Monitoring diseases and other health-related
events over time
 Evaluating the efficacy and effectiveness of
prevention and treatment programs
Selected Activities Performed in
Epidemiology
 Providing information useful in health planning
and decision making for establishing health
programs with appropriate priorities
 Assisting in carrying out public health programs
 Being a resource person
 Communicating public health information
Epidemiology in public health practice
and individual decision making
 Epidemiological findings contribute to
 Preventing and controlling disease, injury,
disability, and death
 How?
 By providing information that leads to informed
public health policy and planning, as well as
individual health decision making
Selected Types of Epidemiologic
Information
 Public health assessment
 Causes of disease
 Completing the clinical picture
 Program evaluation
 Efficacy
 Effectiveness
Questions That Need Epidemiology
 Diagnosis
 Is there such a problem as myalgic encephalitis?
 Is prostate specific antigen a good test for prostate
cancer?
 Causes
 Why did this patient suffer a stroke?
 Is obesity the cause of metabolic syndrome?
Questions That Need Epidemiology
 Treatment
 Is this the best treatment for Parkinson’s disease?
 Is my surgery as good as that of everyone else?
 Prognosis
 What are the chances of a recurrent heart attack?
 How long will this knee joint prosthesis last?
Questions That Need Epidemiology
 Health promotion and protection
 Do current school meals harm children’s future
health?
 Will the Irish smoking ban in public places work
better than the English policy?
 Health and disease surveillance
 Why are there tenfold international differences in
suicide rates?
 When will the next influenza pandemic occur?
Questions That Need Epidemiology
 Health inequalities
 Why should life expectancy be nearly five years
lower in unskilled manual workers?
 Do health services reduce or increase health
inequalities?
Epidemic, Endemic, and Pandemic
 Epidemic – Health-related state or event in a
defined population above the expected, over a
given period of time
 Endemic – Persistent, usual, expected healthrelated state or event in a defined population
over a given period of time
 Pandemic – Epidemic affecting a large number
of people, many countries, continents, or regions
Common Source, Propagated,
and Mixed Epidemics
 Common source
 Point
 Intermittent
 Continuous
 Propagated
 Spread from person to person
 Mixed epidemics
 A mixture of common source and mixed
Common Source
 Tend to result in more cases occurring more
rapidly and sooner than host-to-host epidemics
 Identifying and removing exposure to the
common source typically causes the epidemic to
rapidly decrease
Common Source
 Examples
 Anthrax, traced to milk or meat from infected
animals
 Botulism, traced to soil-contaminated food
 Cholera traced to fecal contamination of food and
water
Propagated
 Arise from infections being transmitted from one
infected person to another
 Transmission can be through direct or indirect
routes
 Host-to-host epidemics rise and fall more slowly
than common source epidemics
Propagated
 Examples
 Tuberculosis
 Whooping cough
 Influenza
 Measles
Mixed Epidemics
 Occurs when a common source epidemic is
followed by person-to-person contact and the
disease is spread as a propagated outbreak
 Example – Shigellosis occurred among a group
of 3,000 women attending a music festival. Over
the next few weeks, subsequent generations of
shigella cases spread by person-to-person
transmission from festival attendees.
Disease Transmission
 Disease transmission usually occurs by
 direct, person-to-person contact (e.g., STDs)
 fomite-borne (e.g., Hepatitis A spread by a
contaminated eating utensil)
 vehicle-borne (e.g., HIV/AIDS spread through
needle sharing drug users)
 vector-borne (e.g., Malaria spread through
mosquitoes)
Accurate Assessment Requires a
Standard Case Definition
 A standard set of criteria, or case definition,
assures that cases are consistently diagnosed,
regardless of where or when they were identified
and who diagnosed the case
Concepts and Principles of Case as
Used in Epidemiology
 A case is a person who has been diagnosed as
having a disease, disorder, injury, or condition
Primary Case, Index Case
 The first disease case in the population is the
primary case
 The first disease case brought to the attention of
the epidemiologist is the index case
 The index case is not always the primary case
Secondary Case
 Those persons who become infected and ill after
a disease has been introduced into a population
and who become infected from contact with the
primary case
Different Levels of Diagnosis
 Suspect
 An individual who has all of the signs and
symptoms of a disease or condition, yet not
diagnosed
 Confirmed
 All criteria met
Different Levels of Diagnosis
 As more information (e.g., laboratory results)
becomes available to the physician, he or she
generally upgrades the diagnosis. When all
criteria are met and they meet the case
definition, the case is classified as a confirmed
case.
Epidemiology Triangle for
Infectious Disease
Triangle is based on the
communicable disease model
 Shows the interaction and interdependence of
agent, host, environment, and time as used in the
investigation of diseases and epidemics.
 Agent – cause of the disease
 Host – an organism, usually a human or an animal, that
harbors a disease
 Environment – includes those surroundings and
conditions external to the human or animal that cause or
allow disease transmission
 Time – accounts for incubation periods, life expectancy
of the host or the pathogen, and duration of the course of
the illness or condition
Stopping an Epidemic
 An epidemic can be stopped when one of the
elements of the triangle is interfered with,
altered, changed, or removed from existence, so
that the disease no longer continues along its
mode of transmission and routes of infection.
Some Disease Transmission
Concepts
 Fomites
 Objects such as clothing, towels, and utensils that
may harbor a disease agent and are capable of
transmitting it; usually used in the plural
 Example – transmission of cutaneous anthrax
from drums to an individual
Vector
 An invertebrate animal (e.g., tick, mite, mosquito,
bloodsucking fly) capable of transmitting an
infectious agent among vertebrates
 Transmission can be mechanical (agent does not
undergo physiologic changes within the vector) or
biological (agent undergoes a part of its life cycle
within the vector before transmission to new host)
 Can spread an infectious agent from an infected
animal or human to other susceptible animals or
humans through its waste products, bite, or body
fluids, or indirectly through food contamination
Reservoir
 The habitat (living or nonliving) on which an
infectious agent lives, grows, multiplies, and
depends on for its survival in nature
 Humans, animals, food, feces, decaying organic
matter
 Humans often serve as both reservoir and host
Zoonosis
 When an animal transmits a disease to a human
 Examples – rabies, Rocky Mountain spotted
fever, shigellosis
Carrier
 A carrier contains, spreads, or harbors an
infectious organism
 Example – Typhoid Mary
 Five types of carriers
Carrier
 Active – Individual has been exposed and has
been harboring disease-causing pathogen; may
or may not be recovered
 Convalescent – Individual in recovery from
disease who is still infectious
 Healthy – Individual has been exposed and
harbors disease-causing pathogen but shows no
symptoms
Carrier
 Incubatory – Individual has been exposed and is
harboring disease-causing pathogen in
beginning stages of the disease, has symptoms,
and is infectious
 Intermittent – Individual in recovery from disease
who is still infectious in different places or time
intervals
Modes of Disease Transmission
 Direct transmission – Direct physical contact
such as touching with contaminated hands, skinto-skin contact, kissing, or sexual intercourse
 Indirect transmission – Occurs when pathogens
or agents are transferred or carried by some
intermediate item, organism, means, or process
to a susceptible host, resulting in disease
Advanced epidemiology triangle for
chronic diseases and behavioral
disorders
Chain of Infection
 Disease transmission occurs when pathogen
leaves the reservoir (e.g., food, water, feces,
animal) through a portal of exit (mucous,
membranes, wounds) and is spread by a mode of
transmission (direct or indirect). Pathogen then
enters the body through a portal of entry (mucous
membranes, wounds) and infects susceptible host.
Chain of Infection
Other Models of Causation
 Rothman’s Causal Pies
Active Primary Prevention
 Requires behavior change on part of subject
 Wearing protective devices
 Health promotion
 Lifestyle changes
 Community health education
 Ensuring healthy conditions at home, school, and
workplace
Passive Primary Prevention
 Does not require behavior change
 Vitamin-fortified foods
 Fluoridation of public water supplies
Secondary Prevention
 Occurs to reduce the progress of disease
 The disease already exists in the person
 Cancer screening – Cancer already present; the
goal is to detect the cancer before clinical
symptoms arise in order to improve prognosis
and prevent conditions from progressing and from
spreading
Tertiary Prevention
 To reduce the limitation of disability from
disease
 The disease has already occurred
 Physical therapy for stroke victims
 Halfway houses for recovering alcoholics
 Shelter homes for the developmentally disabled
 Fitness programs for heart attack patients