Download Epidemiology

Epidemiology in Community Health Care
Epidemiology in Community
Health Care
Prepared by Suhail AL Humoud
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Epidemiology in Community Health Care: objective
After completion the lecture the students enable to:
 Explore the historical roots of epidemiology.
 Explain the host, agent, and environment model.
 Describe theories of causality in health and illness.
 Explain a “web of causation” matrix that assists you with
recognition of multicausal factors in disease or injury occurrences.
 Define immunity and compare passive immunity, active immunity,
cross-immunity, and herd immunity.
 Explain how epidemiologists determine populations at risk.
 Identify the four stages of a disease or health condition.
 List the major sources of epidemiologic information.
 Distinguish between incidence and prevalence in health and
illness states.
 Use epidemiologic methods to describe an aggregate’s health.
 Discuss the types of epidemiologic studies that are useful for
researching aggregate health.
 Use the seven-step research process when conducting an
epidemiologic study.
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definition
DEFINITION
Epidemiology is the study of the
determinants and distribution of health,
disease, and injuries in human
populations.
It is a specialized form of scientific
research that can provide health care
workers, including community health
nurses, with a body of knowledge on
which to base their practice and methods
for studying new and existing problems.
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Definition …. Cont
Epidemiologists
 What is the occurrence of health and disease in a
population?
 Has there been an increase or decrease in a health
state over the years?
 Does one geographic area have a higher frequency of
disease than another?
 What characteristics of people with a particular
condition distinguish them from those without the
condition?
 What factors need to be present to cause disease or
injury?
Is one treatment or program more effective than
another in changing the health of affected people?
 Why do some people recover from a disease and others
do not?
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Definition …. Cont
 Health Indictors
Definition:
Health indicators are standardized measures by
which to compare health status and health system
performance and characteristics among different
jurisdictions in country
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Definition …. Cont
 Categories of Health Indictors
Categories of health indictors
Mortality and burden of disease Ex: Access data on life expectancy,
child mortality, morbidity..
 Health services coverage Ex: Access data on skilled birth
attendance, antenatal care, TB detection/treatment...
 Health systems resources Ex: Access data on health workforce,
hospital beds and health expenditure.
 Risk Factors Ex: Access data on water and sanitation, nutrition,
tobacco use...
 Inequities Ex: Access data on inequities in health care and health
outcome.
 Demographic and socioeconomic statistics as:
Access data on total population, birth/death registration
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Goal of the epidemiology
Goal of the epidemiology
The ultimate goals of epidemiology are to:
1. determine the scale and nature of human health
problems,
2. identify solutions to prevent disease, and
3. improve the health of the entire Population
Epidemiology offers community health nurses a
specific methodology for assessing the health of
aggregates. Furthermore, it provides a frame of
reference for investigating and improving clinical
practice in any setting.
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Goal of the epidemiology … cont
For example, if a community health nursing goal is to
lower the incidence of sexually transmitted diseases
(STDs) in a given community, such a prevention plan
requires information about population groups.
How many STD cases have been reported in this
community in the past year?
What is the expected number of STD cases (the
morbidity rate)?
Which members of the community are at highest risk
of contracting STDs?
Any program of screening, treatment, or health
promotion regarding STDs must be based on this kind of
information about population groups to be effective.
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Goal of the epidemiology
Florence Nightingale, the first nurse epidemiologist,
pioneered the use statistics to improve public health.
During the Crimean War, Nightingale collected data and
systemized record-keeping practices to improve hospital
conditions. She invented pie charts, and other graphical
illustrations to depict mortality rates and show how
improvements in sanitary conditions would lead would
lead to decrease in deaths. By focusing on health and
disease trends among populations. Ms. Nightingale saved
or improved the lives of countless individuals, the
ultimate goal of epidemiology.
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Definition of related concept
An epidemic refers to a disease occurrence that
clearly exceeds the normal or expected frequency in a
community or region.
Epidemics: infections affecting a large number of people
at the same time.
- Examples:
- In past centuries, epidemic of cholera, smallpox swept
through community after community , killing thousands of
people, changing the community structure.
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Definition of related concept
Pandemic:
An epidemic that worldwide in distribution.
- Pandemic: infections affecting extremely high
numbers of people, usually in many countries.
Examples: -Acquired Immunodeficiency
Syndrome (AIDS) is worldwide in distribution.
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Definition of related concept
Endemic:
The continuing presence of a disease or
infectious agent in a given geographic area.
Examples:
 Plague in Vietnam.
 Malaria in the tropic of, Africa, Brazil and
Indonesia.
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Definition of related concept
Biostatistics:
Is the science of statically measuring
population health condition.
- Biostatistics are the primary public health
measurement and analytic science underlying
community health practice.
- Biostatistics helps to describe the extent and
distribution of health, illness, and conditions in
the community.
- Biostatistics aids in the identification of
specific health problems and community
strengths.
- It facilitates the setting priorities for
program planning.
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Definition of related concept
A few Statistics
Rate, ratio, incidence, and prevalence are common terms
used to help describe illness and disease among population
groups.
A rate: A statistical measures expressing the
proportion of persons with a given health
problem among a population at risk.
Number of events
A rate is= --------------------X100,000
Population at risk
.
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Definition of related concept
A ratio:
which is simply the comparison of one number
with another.
A ratio: is often used to compare one atrisk population with another.
The number of females: The number of
males
.
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Definition of related concept
Mortality: Death rate.
Morbidity: Illness rate.
Mortality and morbidity statistics are
collected routinely and used as indicators of the
frequency of deaths and disease as they occur in
time, place, and persons.
.
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Definition of related concept
Incidence and Prevalence Rates
Incidence: Refers to the rate at which a specific
disease develops in a population.
An incidence rate is the number of new cases of an
illness or injury that occurs in a specific time.
Number of persons developing a disease
Incidence rate=------------------------------------- X 100,000
Total number at risk per unit of time.
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Definition of related concept
Prevalence: measures all of the existing cases at a
given point of time.
Prevalence includes the incidence (new cases) plus all of
the existing cases.
The prevalence rate is influenced by how many people
become ill, and by the number of people who die, or do
not recover.
Number of persons developing a disease
Prevalence rate= ---------------------------------X100,000
Total number at risk per unit of time
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CONCEPTS BASIC TO EPIDEMIOLOGY
CONCEPTS BASIC TO EPIDEMIOLOGY
The science of epidemiology draws on certain
basic concepts and principles to analyze and
understand patterns of occurrence among
aggregate health conditions.
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CONCEPTS BASIC TO EPIDEMIOLOGY
I. Host, Agent, and Environment Model
Host, Agent, and Environment Model
Through their early study of infectious
diseases, epidemiologists began to
consider disease states generally in
terms of the epidemiologic triad, or the
host, agent, and environment model.
Interactions among these three
elements explained infectious and other
disease patterns.
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Host, Agent, and Environment Model …. cont
The host is a susceptible human or animal who
harbors and nourishes a disease-causing agent.
Many physical, psychological, and lifestyle factors
influence the host’s susceptibility and response to an
agent.
Physical factors include age, sex, race, and genetic
influences on the host’s vulnerability or resistance.
Psychological factors, such as outlook and response to
stress, can strongly influence host susceptibility.
Lifestyle factors also play a major role. Diet,
exercise, sleep patterns, and healthy or unhealthy
habits all contribute to either increased or decreased
vulnerability to the disease-causing agent..
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Host, Agent, and Environment Model …. cont
Agent is a factor that causes or contributes to
a health problem or condition.
Causative agents can be factors that are present
(eg, bacteria that cause tuberculosis, rocks on a
mountain road that contribute to an automobile
crash) or factors that are lacking (eg, lack of iron
in the body that causes anemia; lack of seat belt
use that contributes to the extent of injury during
an automobile crash).
Agents vary considerably and include five types:
biologic, chemical, nutrient, physical, and
psychological. Biologic agents include bacteria,
viruses, fungi, protozoa, worms, and insects.
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Host, Agent, and Environment Model …. cont
The environment refers to all the external factors
surrounding the host that might influence vulnerability or
resistance.
The physical environment includes factors such as
geography, climate, weather, safety of buildings, water and
food supply, and presence of animals, plants, insects, and
microorganisms that have the capacity to serve as
reservoirs (storage sites for disease-causing agents) or
vectors (carriers) for transmitting disease.
The psychosocial environment refers to social, cultural,
economic, and psychological influences and conditions that
affect health, such as access to health care, cultural
health practices, poverty, and work stressors, which can all
contribute to disease or health.
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Host, Agent, and Environment Model …. cont
Host, agent, and environment interact to cause a
disease or health condition.
For example, the agent responsible for Lyme disease
is the spirochete Borrelia burgdorferi;
humans of all ages are susceptible hosts, along with
dogs, cattle, and horses. Ticks that feed on wild
rodents and deer transfer the spirochete to human
hosts after feeding on them for several hours.
Environmental factors, such as working or playing in
tick-infested areas, influence host vulnerability.
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CONCEPTS BASIC TO EPIDEMIOLOGY
II. Causality
Causality refers to the relationship between a
cause and its effect.
A purpose of epidemiologic study has been to
discover causal relationships, so as to
understand why conditions develop and offer
effective prevention and protection. Over the
years, however, as scientific knowledge of
health and disease has expanded,
epidemiology has changed its view of causality
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CONCEPTS BASIC TO EPIDEMIOLOGY
III. Immunity
Immunity refers to a host’s ability to resist a
particular infectious disease–causing agent. This
occurs when the body forms antibodies and
lymphocytes that react with the foreign
antigenic molecules and render them harmless.
For community health nursing, this concept has
significance in determining which individuals and
groups are protected against disease and which
may be vulnerable. Four types of immunity are
important in community health: passive immunity,
active immunity, cross-immunity, and herd
immunity.
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Immunity
1. Passive immunity refers to short-term
resistance that is acquired either naturally
or artificially. Newborns, through maternal
antibody transfer, have natural passive
immunity that lasts about 6 months.
Artificial passive immunity is attained
through inoculation with a vaccine that gives
temporary resistance.
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Immunity
2. Active immunity is long-term and
sometimes lifelong resistance that is acquired
either naturally or artificially. Naturally
acquired active immunity comes through host
infection.. Artificially acquired active
immunity is attained through vaccine
inoculation. Such vaccines are prepared
from killed, living-attenuated, or livingvirulent organisms administered to artificially
produce or increase immunity to a particular
disease.
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Immunity
3. Cross-immunity refers to a situation in
which a person’s immunity to one agent
provides immunity to another related agent as
well. The immunity can be either passive or
active. Sometimes, infection with one disease,
such as cowpox, gives immunity to a related
disease, such as smallpox..
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Immunity
4. Herd immunity describes the immunity level
that is present in a population group (Chin,
1999). A population with low herd immunity is
one with few immune members; consequently,
it is more susceptible to the disease.
Nonimmune people are more likely to contract
the disease and spread it
throughout the group, placing the entire
population at greater risk...
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CONCEPTS BASIC TO EPIDEMIOLOGY
Risk
To determine the chances that a disease or
health problem will occur, epidemiologists are
concerned with risk, or the probability that a
disease or other unfavorable health condition
will develop.
For any given group of people, the risk of
developing a health problem is directly
influenced by their biology, environment,
lifestyle, and system of health care
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Risk … cont
A population at risk is a collection of people
among whom a health problem has the
possibility of developing because certain
influencing factors are present (eg, exposure
to HIV) or absent (eg, lack of childhood
immunizations, lack of specific vitamins
in the diet), or because there are modifiable
risk factors (eg, with cardiovascular disease).
Incidence in exposed group
Relative risk ratio = -----------------------------Incidence in unexposed group
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Sources of information for epidemiological study
SOURCES OF INFORMATION
Epidemiologic investigators may draw data from
any of three major sources:
(1) existing data,
(2) informal investigations,
(3) scientific studies.
The community health nurse will find all three
sources useful in efforts to improve the health
of aggregates.
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Existing Data
1) Existing Data
A variety of information is available nationally, by
state, and by section, such as county, region, or
urbanized area. This information
a. Vital Statistics
Vital statistics refers to the information gathered from
ongoing registration of births, deaths, adoptions,
divorces, and marriages. Certification of births,
deaths, and fetal deaths are the most useful vital
statistics in epidemiologic studies
Sources for vital statistical information include state
Web sites on the Internet, local and state health
departments, city halls, and county halls of records
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Existing Data
b. Census Data
Data from population censuses taken every 10 years in
many countries are the main source of population
statistics. This information can be a valuable assessment
tool for the community health nurse who is taking part in
health planning for aggregates.
Population statistics can be analyzed by age, sex,
race, ethnic background, type of occupation, income
gradient, marital status, educational level, or other
standards, such as housing quality. Analysis of population
statistics can provide the community health nurse with a
better understanding of the community and help identify
specific areas that may warrant further epidemiologic
investigation. Data from the KSA. Census Bureau is
found on their Web site.
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Existing Data
c. Reportable Diseases
Each state has developed laws or regulations that
require health organizations and practitioners to report
to their local health authority cases of certain
communicable and infectious diseases that can be
spread through the community. This reporting enables
the health department to take the most appropriate
and efficient action. All states require that diseases
subject to international quarantine regulations
be reported immediately.
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Existing Data
d. Disease Registries
Some areas or states have disease registries or
rosters for conditions with major public health
impact. Tuberculosis and rheumatic fever registries
were more common when these diseases occurred
more frequently. Cancer registries provide useful
incidence, prevalence, and survival data and assist
the community health nurse in monitoring cancer
patterns within a community. Community health nurses
can access these registries through state health
department Web sites.
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Existing Data
e. Environmental Monitoring
State governments, through health departments or other
agencies, now monitor health hazards found in the
environment. Pesticides, industrial wastes, radioactive or
nuclear materials, chemical additives in foods, and
medicinal drugs have joined the list of pollutants
Concerned community members and leaders view these as
risk factors that affect health at both community and
individual levels. Community health nurses can also obtain
data from federal agencies such as the Food and Drug
Administration, the Consumer Product Safety Commission,
and the Environmental Protection Agency.
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Sources of information for epidemiological study
2) Informal Observational Studies
A second information source in epidemiologic study is
informal observation and description. Almost any client
group encountered by the community health nurse can
trigger such a study.
3) Scientific Studies
The third source of information used in epidemiologic
inquiry involves carefully designed scientific studies.
The nursing profession has recognized the need to
develop a systematic body of knowledge on which to
base nursing practice. Already, systematic research is
becoming an accepted part of the community health
nurse’s role. Findings from epidemiologic studies
conducted by or involving nurses are appearing more
frequently in the literature
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Method in the epidemiologic investigation process
METHODS IN THE EPIDEMIOLOGIC
The goals of epidemiologic investigation are to identify the
causal mechanisms of health and illness states and to
develop measures for preventing illness and promoting
health. Epidemiologists employ an investigative process
that involves a sequence of three approaches that build on
one another: descriptive, analytic, and experimental
studies. All three approaches have relevance for
community health nursing
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Method in the epidemiologic investigation process
Descriptive Epidemiology
includes investigations that seek to observe and describe
patterns of health-related conditions that occur naturally
in a population.
example, a community health nurse might seek to learn how
many children in a school district have been immunized for
measles, how many home births occur each year in the
county, how many cases of STDs have occurred in the city
in the past month, or how many automobile crashes have
occurred near the community high school. At this stage in
the epidemiologic investigation, the researcher seeks to
establish the occurrence of a problem. Data from
descriptive studies suggest hypotheses for further
testing. Descriptive studies almost always involve some
form of broad-based quantification and statistical analysis.
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Method in the epidemiologic investigation process
Descriptive Epidemiology
1.Counts
2.Rates
a. incidence rate
b. prevalence rate
c. period prevalence rate
Crude Mortality Rate
Cause-Specific Mortality Rate
Case Fatality Rate
Proportional Mortality Ratio
Age-Specific Mortality Rate
3. Computing Rates
3:1 mortality rate
3:2 morbidity rate
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Method in the epidemiologic investigation process
Analytic Epidemiology
A second type of investigation, analytic
epidemiology, goes beyond simple description or
observation and seeks to identify associations
between a particular human disease or health
problem and its possible causes. Analytic studies
tend to be more specific than descriptive studies in
their focus
Prevalence Studies
Case-Control Studies
Cohort Studies
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Method in the epidemiologic investigation process
Experimental Epidemiology
Experimental epidemiology follows and builds on
information gathered from descriptive and analytic
approaches. It is used to study epidemics, the etiology
of human disease, the value of preventive and
therapeutic measures, and the evaluation of health
services (Valanis, 1999). In an experimental study, the
investigator actually controls or changes the factors
suspected of causing the health condition under study
and observes what happens to the health state. In
human populations, experimental studies should focus
on disease prevention or health promotion rather than
testing the causes of disease, which is done primarily
on animals.
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