2. Objectives
1. Define epidemiology (Epi)
2. Describe how epidemiology has developed over
time
3. Describe the essential elements of Epi and an
epidemiological approach
4. Explain the basic Epidemiological concepts
5. Differentiate between descriptive and analytical
epidemiology
6. Explain how nurses use epidemiology in
community health practice
7. Identify terms that are used to measure and
characterize disease frequency in human
populations
2
3. How is Public/Community Health Different
From Medicine?
• Public health is
population-
based
• Medicine is
based on the
individual
3
4. 4
Epidemiology
• The study of the distribution of health and
illness and the factors that determine
(determinants) the population’s health status
5. Purpose of Epidemiology
• To search for causal relationships in health and
illness
• To control illness by understanding causality
Goal: Preventing disease and maintaining health
5
7. Goals
7
Medical Care
Individual Health
Public Health
Population Health
Best outcome for
individual
Healthy community
Balance of individual
autonomy vs. limitations
on individual
Balance in allocation of
resources
Focus on prevention
8. Analytic Epidemiology
• Investigates origins and causal factors
• Looks at etiology
• Looks at factors, exposures, characteristics and
behaviors
• Why are some affected more than others
Example – Smoking……………
9. Analytic Epidemiology
• Search for determinants of disease or injury
• Research on cause-effect relationships that tests
specific hypotheses:
▫ Case-control studies
▫ Cohort studies
▫ Randomized clinical trials
9
10. Descriptive Epidemiology
• Looks at health outcomes in terms of who, what
where, when and why.
• Discusses diseases in terms of person, place and
time.
Example – H1N1 ………………
11. Descriptive Epidemiology
• Studies the distribution of disease and other
health-related states and events in terms of:
▫ personal characteristics, (person)
▫ geographical distribution (place), and
▫ temporal patterns (time).
11
12. Patterns Relative to Person
• Age
• Education
• Race
• Gender
• Occupation
• Income
• Ethnicity
• Behavior
Person: Who has the lowest /
highest disease rates in the
population?
12
13. Descriptive Epidemiology: Patterns of
Health Events
Patterns Relative to Place
• Where (place) is the health outcome occurring
most frequently?
13
14. Patterns Relative to Place
• Define in terms of traditional political
boundaries
▫ States
▫ Counties
▫ Municipalities
• Census track data/zip codes
14
15. Descriptive Epidemiology
• geographic unit
▫ state
▫ county
▫ census tract
15
population density
migration
Place: Where are the lowest / highest
disease rates for a population?
18. Descriptive Epidemiology
• short-term trends
• long-term or
secular trends
18
cyclic trends
age, period, and
birth cohort
effects
Time: Are the disease rates changing
over time for a population?
19. Patterns Relative to Time
• Is the frequency of the health outcome changing
over time?
19
20. Patterns Relative to Time
• Annual trends
• Seasonal occurrence
• Daily or hourly changes
20
22. Descriptive Epidemiology (DE)
• Used to understand the pattern and frequency of
health events in a population, e. g., childhood
asthma
22
How often are kids
hospitalized for asthma
compared to other
conditions?
Which groups are at high
risk for being hospitalized
for asthma?
Are childhood
asthma
hospitalization
increasing or
decreasing?
Identify emerging problems and track known public health issues (CH
Nurse)
23. Descriptive Epidemiology
• Prioritize public health problems
• Target resources and interventions
• Provides information for policy and
program development
• Evaluate programs and practices
• Advocate for additional resources
▫ Human Resources
▫ Financial and physical resources
23
24. Epidemiology: Two broad concepts
• Control of health problems through an
understanding of their contributing factors
• Application of epidemiologic techniques to
health-related conditions other than acute
communicable disease
24
25. Epidemiology: Causality and Control
• Health Outcomes are characterized in terms of:
▫ What is the outcome?
▫ Who is affected?
▫ Where are they?
▫ When do events occur?
▫ Why?
25
28. Epidemiologic Triangle (Box 9-1; p. 168)
• Agent- animate or inanimate factor that must be
lacking or present for a disease or condition to
develop
• Examples:
▫ Infectious agents: virus, bacteria
▫ Chemical agents: pesticides
▫ Physical agents: radiation, heat, machinery
28
29. Epidemiologic Triangle
• Host – human or animal species capable of
being infected and affected by an agent
• Examples:
▫ Genetic susceptibility
▫ Age, sex
▫ Acquired characteristics (immunological status)
▫ Life style factors
29
30. Epidemiologic Triangle
• Environment - all that is internal or external to
a given host or agent and that is influenced and
influences the host and/or agent
• Examples:
▫ Climate
▫ Plant and animal life
▫ Socio economic status
▫ Populations – distribution and density
30
31. Determinants of health events
• The determinants of health events refers to those
factors, exposures, characteristics, behaviors,
and contexts that determine or influence the
patterns.
▫ How does it occur?
▫ Why are some affected more than others?
Individual
Relational or social
Communal or environmental
31
32. Determinants
• Focus is on investigation of causes and
associations (analytic epidemiology)
• Understanding the etiology or natural history of
the disease
32
33. Distribution
• Refers to patterns of health events in
populations.
• Health-related events in human populations :
▫ Diseases
▫ Conditions
▫ Injuries
33
34. CH Nurse and Epidemiology
• Epidemiologist—a
health detective who
links observed
problems with
potential causes, to
arrive at a diagnosis
and design and
implement a
mitigating response.
34
35. How CHN Use Epidemiology
• Identifying causative factors
• Identifying risk factors
• Diagnosing the health status of population
groups
• Describing S & S and the course of a disease
• Evaluating the effectiveness of existing and
proposed interventions and modes of health care
delivery
• Providing a basis for health policy
35
37. Causality
• One event is the result of another event
• Theories of causation (single cause)
▫ Religious Era - disease caused by punishment
▫ Environmental Era – disease caused by harmful
substances in the environment
▫ Bacteriologic Era – disease caused by specific
organisms
▫ Current Era – multiple causation
37
38. Causality: Example
• Important to know the potential for various
sources of exposure
• Evidence-based
▫ Lead:
Paint
Water pipes
Contaminated Soil
38
39. Criteria for Determining Causality
• Consistency of association
• Strength of association
• Specificity
• Temporal relationship between
events
• Coherence with other known facts
39
40. Determining Causality: Criteria
1. Consistency of association
▫ Association between the factor in
question and the problem must be
consistent
• Example:
▫ People can not develop measles
without being exposed to the virus
40
41. Determining Causality: Criteria
2. Strength of association
▫ The greater the correlation between
the occurrence of the factor and the
health condition, the greater the
association (cause and effect)
• Example:
▫ Measles: some develop it some don’t
41
42. Determining Causality: Criteria
• Strength of the association may reflect:
▫ Dose-response gradient - the greater the
exposure to the presumed cause, the greater the
likelihood of developing the problem (Gordis,
2000)
42
43. Criteria for Determining Causality
3. Specificity – present when the factor
in question results in one specific
condition
• Example: exposure to the measles
virus result only in measles not in
mumps of chickenpox
43
44. Criteria for Determining Causality
4. Temporal relationship between
events:
▫ Refers to the time relationship between
the factor and the resulting condition
• Example: one must be exposed to
measles virus before, not after, one
gets the measles
44
45. Criteria for Determining Causality
5. Coherence with other known facts:
▫ The idea that one condition causes another must
be logical and congruent with other known facts.
• Example: alcohol consumption and car accidents
▫ Increases the time required for voluntary muscles
to react to stimuli
▫ Slow response to changing driving conditions
▫ Causative factor in many accidents
45
46. Epidemiological Key Terms (WHO)
▫ Epidemic: An outbreak of a
contagious disease or condition that
spreads rapidly and widely.
46
47. Epidemiological Key Terms
• Endemic: of or relating to a disease (or
anything resembling a disease) constantly
present to greater or lesser extent in a particular
locality;
• Examples of endemic diseases/conditions:
"endemic malaria“ in the tropics
"food shortages and starvation are endemic in
certain parts of the world“
Botulism in Alaska
Cholera among some Asian/Pacific Islanders
47
48. Epidemiological Key Terms
• Point epidemic: a time-and-space-related
pattern which is an indicator for toxic exposures.
▫ Outbreak of a GI illness due to contaminated food
• Example: E-coli infection due to contaminated
spinach in summer 2007 in Western USA
48
49. Epidemiological Key Terms
▫ Pandemic - an epidemic that is
geographically widespread or over a
wide geographical area; occurring
throughout a region or even
throughout the world
AIDS in Africa
49
53. Measures of Morbidity and Mortality
• Rates –Frequency of a health event
• Proportions – Fraction of population affected
• Risk –Probability that an event will occur
54. Rates (Rates of Occurrence)
• Rates of occurrence are statistical measures that
indicate the extent of health problems in a group
• An expression of events relative to the size of the
population in which they occurred.
• Enables us to compare the risk of health events
across different groups of people, places, and
time periods
54
56. Rates
A measurement of the frequency of a health
event in a specific population over a specific
period of time
• Mortality rate is expressed as an annual death
rate or mortality rate from all causes:
Total no. of deaths from all causes in 1 yr. X 1,000
No. of persons in the population at mid year
57. Expression of Rates
• Rate is a measure of a part
• A portion of the population experiencing an
event
• It is expressed per 1,000 people because that is
easier to relate to 51 per 1,000 rather than 0.051
cases per person
58. Case Fatality Rate
Case fatality is the number of people who die of a disease
over the total number of people with the disease.
Die from disease X 100
Total with disease
Find the case fatality rate for 20 women diagnosed with
ovarian cancer if 18 die in one year.
59. Crude Rates
• Total number of events divided by total
population
• For mortality, crude rates can either be deaths
from all causes OR cause-specific (e. g., deaths
from coronary heart disease)
59
60. 60
Crude Rates: Total Mortality
Place Total
Death
Population Rate per
100K
Mercer
Island
(1991-95)
736 103,805 709.0
Snoqualamie
Valley
(1991-95)
707 157,750 448.2
61. Problem with Crude Rates
• They don't account for underlying demographic
differences
AGE
LOCATION
TIME
62. 62
Age-adjusted rates
• Age-adjustment is a statistical process applied to
rates of disease, death, injuries or other health
outcomes that allows communities with different
age structures to be compared.
63. 63
Age-Adjusted Rates
• Applies the observed age-specific rates to a
standard population
▫ 1950 U.S. population
▫ 2000 projected U.S. population
• Represents the hypothetical rate that would
have been observed if the population of interest
had the same age distribution as the standard
population
64. What rates tell us
• How quickly things are happening
• How things are changing
• Moving form one state of being to another
65. Proportion
• Example: In 2008, there were 31,753,000
persons 65 or older in a population of 252,
177,000
31,753,000
__________
252,177,000 = .126 or 12.6%
65
66. Deaths per live Births
• A proportion that indicates the portion of a
population who experience an event during
some specified period of time, e.g. the annual
infant mortality rate.
66
67. Incidence
• The incidence of disease is the number of NEW
cases of a disease that occur within a specified
time period.
• Expressed as a fraction:
Number of new cases of a disease occurring in the
population during a specified period of time
______________________________ X 1,000
Number of persons at risk of developing the disease during
that time period
68. Incidence Rate
• Example 1
• Incidence rate = 5 new people with a diagnosis of HIV=
0.50
• Population of 10 people
• Example 2:
• Incidence rate = 5 new people with a diagnosis of HIV=
0.05
• Population of 100 people
• 5% or 5 of 100 people
68
69. 69
Incidence Rates
• It is very important to know the number of new
people infected with a disease (incidence) in
relation to the total population at risk of
contracting that disease *during a specified time
period.
*Point Prevalence
70. Incident Rates
• Tell us 3 things
The occurrence of NEW cases during a specified
time period
QUANITFIES the rate of development of NEW cases
Tells us the probability that a person at risk will
develop the disease
71. Prevalence Rates
• Measures the presence of a disease or
attribute in a population at a given
time (Point Prevalence)
• Probability that an individual in the
population has a disease/condition
71
72. 72
Prevalence data
• Provide an indication of the extent of a condition
and may have implications to the provision of
services needed in a community.
• Prevalence is most useful for measuring the
burden of chronic diseases such as tuberculosis,
malaria and HIV in a population.
73. Calculate HIV Prevalence Rate
• In 2003 (specific point in time) Clinic B gave
service to 1000 patients (population at risk)
• 200 of these patients were HIV +
• The HIV prevalence rate among the clinic’s
patients at the end of 2003:
▫ Existing # of pt. with HIV = 200
▫ Divided by population at risk 1000
= 0.20 (20%)
73
74. 74
Examples of Prevalence Rates
• Disease/violence risk factors (e.g., tobacco use,
firearm ownership)
• Health care access (e.g., health insurance
coverage, unmet medical need)
• Health screening (e.g., mammography. Pap test,
cholesterol, blood pressure)
76. 76
Distinguishing between I & P*
• Incidence gives us a barometer of how many new
cases of a disease are being detected,
• While prevalence gives us a barometer of how
long people are living with a disease.
*I: Incidence
*P: Prevalence
77. 77
Hepatitis A Cases: Hypothetical
Location # of Cases Time
Period
Annual
Population
Union
County
33 1992-95 17,715
Essex
County
44 1994-95 394,923
Where is the risk of Hepatitis A higher?
78. 78
Hepatitis B occurred more frequently in
which County?
Location # of
Cases/Pop/Year
Average Annual Rate
Orange
County
33/ 17,715/3 years
(11 cases per year,
on average)
62.1 / 100,000 people per
year
Dale
County
55/394,923/3 years
(22 cases over 2
years, on average)
46.4 / 100,000 people per
year
*When comparing rates in different places use the same time period
for each place.
79. 79
• Public health surveillance is the ongoing
collection and timely analysis, interpretation,
and communication of health information for
public health action
• Public health surveillance systems are
important tools for collecting and
disseminating descriptive epidemiologic data
Surveillance
80. 80
Surveillance
Method
• population-based
• representative sample
• convenience sample
Example
-- vital statistics
-- BRFSS
-- survey at local mall
Different surveillance collection methods
provide varying levels of confidence in the
data.
81. 81
Sampling
Types
• Simple random sampling = every sampling
unit has an equal chance of being sampled
• Systematic sampling = every ith sampling
unit is sampled
84. 84
Surveillance Data on the Internet
• Centers for Disease Control and Prevention
(www.cdc.gov)
▫ CDC Wonder
▫ Behavioral Risk Factor Surveillance System
• National Center for Health Statistics
(www.cdc.gov/nchs)
86. 86
National Center for Health Statistics
(NCHS)
• http://www.cdc.gov/nchs
• What parts of this site are useful for fact lookup,
research and indicators?
87. 87
Public Health Surveillance Loop
Data Program
Interpretation Evaluation
Data Information
Program
Analysis Dissemination
Implementation
Data Program
Collection Planning
88. 88
Screening
• Screening is defined as the testing of
groups of individuals who are at risk for
certain conditions but are as yet
asymptomatic.
• CHN strategies
▫ Know latest guidelines
▫ Link to referral mechanisms
▫ Follow-up
90. 90
Validity
• In a screening test is measured in terms of the
probability of correctly classifying an individual
with regard to the disease or outcome of interest
• Usually measured by sensitivity and specificity.
91. 91
Sensitivity
• Quantifies how accurately the test identifies
those with the condition or trait
• Represents the proportion of persons with the
disease whom the test correctly identified as
positive (True Positive)
92. 92
Specificity
• Indicates how accurately the test identifies those
without the condition or trait
• Represents the proportion of persons who do
not have (without) the disease whom the test
correctly identified as negative for the disease
(True Negative)
93. 93
Sensitivity and Specificity
• Determined by comparing the results from the
test with results from a definitive diagnostic
procedures
▫ Diabetes
▫ Pap smear
• Combination of two or more tests are used to
enhance sensitivity or specificity
▫ ELISA and Western Blot tests for HIV
94. 94
Series Testing
• Used to enhance sensitivity or specificity
• Sequence is important
• The final result is considered positive only if all
tests in the series were positive
• It is considered negative if any test was negative
• Series testing enhances specificity, producing
fewer false positives, but sensitivity will be lower
95. 95
Applications of epidemiology in community and public
health nursing.
• Community-oriented nurses work in diverse
settings and agencies, with a range of
responsibilities.
• The practice of community-oriented nursing is
enhanced by the understanding and application
of epidemiological concepts and methods.
96. 96
Applications of epidemiology in community and
public health nursing.
• Epidemiological measures are used to assess the
health needs of a population.
• Planning and implementation of health care
services, interventions, and policies depend on
understanding factors that influence health and
disease and on the ability to evaluate
interventions, programs, and policy.
97. Levels of prevention
• Primary prevention involves interventions to
reduce the incidence or prevent disease by
promoting health and preventing disease
processes from developing.
• CHN Strategies:
▫ General Health Promotion Activities
Health education
Counseling
▫ Prevention
Immunization
97
98. 98
Levels of prevention
• Secondary prevention includes programs
designed to detect disease in the early stages,
before signs and symptoms are clinically
evident, to allow early diagnosis and treatment.
• CHN Strategies:
▫ Health screenings (community settings)
▫ Examples: Diabetes, cholesterol, skin cancer
99. 99
Levels of prevention
• Tertiary prevention provides interventions
directed toward persons with clinically apparent
disease, with the aim of curing, ameliorating the
course of disease, reducing disability, or
rehabilitating.
• Clinics, hospitals, homes
100. 100
Levels of Prevention: Examples
• Primary- Discuss with client low-fat diet and the
need for regular exercise
• Secondary- Implement BP and cholesterol
screening; give treadmill stress test
• Tertiary- Provide cardiac rehabilitation,
medication, out-patient post-cardiac surgery
care, community exercise program
101. 101
Summary
• Epidemiology: is a core component of public
health,
▫ studies populations to understand causes of disease
and to develop and evaluate effective interventions to
prevent disease and maintain health.
▫ multidisciplinary enterprise, encompassing clinical
medicine and laboratory sciences, quantitative
methods, such as biostatistics, and public health policy
and goals.
102. 102
Summary
• Clinical medicine:
▫ focuses on the diagnosis and treatment of disease
in individuals
• Community and public health nursing:
▫ bridges these disciplines in its focus on individual
clients and services, and in its use of
epidemiological methods and findings in
community health nursing practice.
