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Basics to Epidemiology
Introduction
Epidemiology is the study of the determinants, occurrence, distribution,
and control of health and disease in a defined population. It is a
descriptive science and includes the determination of rates, and the
quantification of disease occurrence within a specific population. The
most commonly studied rate is the attack rate: the number of cases of the
disease divided by the population among whom the cases have occurred.
One goal of epidemiologic studies is to define the parameters of a
disease, including risk factors, in order to develop the most effective
measures for control.
It shares with community health nursing the common focus of the health
of population, it provide health professional a body of knowledge on
which to base their practice and methods for studying new existing
problem and to plan and develop measures of control and prevention
programs.
Epidemiology use three investigating approaches; descriptive, analytical
and experimental, all studies can be retrospective or prospective. It also
use of quantitative concept as count, prevalence rate, incidence rate,
mortality rate…etc.
Proper interpretation of disease-specific epidemiologic data requires
information concerning past as well as present occurrence of the disease.
An increase in the number of reported cases of a disease that is normal
and expected, representing a seasonal pattern of change in host
susceptibility, does not constitute an epidemic. Therefore, the regular
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collection, collation, analysis, and reporting of data concerning the
occurrence of a disease is important to properly interpret short-term
changes in occurrence.
Definition
Epidemiology is the study of the determinants, occurrence distribution of
health, diseases and injuries in a defined population.
It Is defined as population science, study the population aggregates and
compares the pattern of disease in population and between places over
time.
The term is derived from Greek words; epi (upon), demos (the people),
logos (knowledge).
Epidemiology is the study of factors affecting the health and illness of
populations, and serves as the foundation and logic of interventions made
in the interest of public health and preventive medicine. It is considered a
cornerstone methodology of public health research, and is highly
regarded in evidence-based medicine for identifying risk factors for
disease and determining optimal treatment approaches to clinical practice.
Epidemiologists attempt to determine what factors are associated with
diseases (risk factors), and what factors may protect people against
disease (protective factors). The science of epidemiology was first
developed to discover and understand possible causes of contagious
diseases like smallpox, typhoid and polio among humans. It has expanded
to include the study of factors associated with non-transmissible diseases
like cancer, and of poisonings caused by environmental agents.
Uses of epidemiology

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


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Determine the primary agent responsible or causative factors
Determine characteristic of agents or the causative factors
Define the mode of transmission
Determine contributing factors
Identify and determine geographic pattern
To describe and report on the natural cause of disease , disability,
injuries and death
 To aid in planning and development of health services
programming
 To provide administrative and planning data
Purpose of Epidemiology
To provides a body of knowledge on which to base the practice and
methods for studying new and existing problem, and assessing the health
of aggregates and improving clinical practice in any setting.
To provide a basis for developing disease control and prevention
measures for groups at risk.
Towards this purpose, epidemiology seeks to
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
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describe the frequency of disease and its distribution
consider person, place, time factors
assess determinants or possible causes of disease
consider host, agent, environment
Issues address by epidemiology: diseases, disabilities, injures, mortality
Epidemiological Models
I.
Epidemiological Triangle: Host, Agent and Environment
Model
The early model used to study the infectious diseases, interaction among
these three elements explained the pattern of infectious diseases and other
diseases.
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Host
Susceptible human, animal that harbors/shelter) and nourishes a disease –
causing /contributing agent.
Several factors affect host response to agents;
 Physical factors as sex, age, and race and genetics influence the
hosts vulnerability or resistance
 Psychological factors as stress
 Life style as diet, exercise sleep pattern.
Personal traits, behaviors,, genetic predispositions, immunological
factors, influence the chance of disease and its severity
Development of disease in a host is influenced by host defense
mechanisms, which may be nonspecific or specific.
 Nonspecific defense mechanisms include the skin, mucous
membranes, secretions, excretions, enzymes, the inflammatory
response, genetic factors, hormones, nutrition, behavioral patterns,
and the presence of other diseases.
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 Specific defense mechanisms or immunity may be natural,
resulting from exposure to the infectious agent, or artificial,
resulting from active or passive immunization.
Agent is factor that causes or contributes to health problem or condition.
Types of Causative agents that necessary for disease to occur
 Biological agents includes, bacteria, viruses , ….
 Chemical agents are liquids, solids, gases, dusts and fumes,,
 Nutrient agent include essential dietary component that can
produce illness condition if they are deficient or taken in excess.
Deficiency of niacin can cause pellagra, excess vitamin. A can be
toxic.
 Physical agent is anything mechanical (automobile), atmosphere as
ultraviolet, geologic as earthquake, and genetics.
 Psychological agents are events that produce stress leading to
health problems.
Classification of agents
 Infectious agents that cause diseases as AIDS and that are
communicable and spread from one to another
 Non infectious agents have the same characteristics in that relative
abilities to harm the host vary with the type of agents and intensity
and duration of exposure.
Environment
External conditions, physical, social or biological, surrounding the host
and contribute to the disease process.
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Physical environment includes factors as geography, climate,
whether, safety of building, water, food supply, animals, plants , insects,
and microorganisms that have the capacity to serve as reservoir (storage
sites for disease-causing agents) or vectors(carriers) for transmitting
disease.
Psychosocial environment refer to social, cultural, economic and
Psychological conditions that affect health as access to health care,
poverty, cultural practices, work stressors.
Host, agent and environment interact to cause the disease, or any
other health condition.
Applying the Epidemiologic Triangle using one of infectious
disease hepatitis A
Hepatitis A is caused by a virus (hepatitis A virus, or HAV) that
multiplies in liver cells and is shed in stool.

The Agent—“What”
The agent is actor that causes or contributes to health problem or
conditions
“agent” for hepatitis A is s hepatitis A virus, or HAV

The
Host—“Who”
Susceptible
human,
animal
that
harbors/shelter) and nourishes a disease – causing agent.
 Age will influence the association because the very young and very
old are more susceptible, as are people with a depressed immune
system or with an. enhanced genetic susceptibility to respiratory
disease.
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People at risk who get , contract the disease are children at school, infant
at nursery and old ages over 70 years old , in some restaurants’

The Environment—“Where”
The environment is the favorable surroundings and conditions outside the
host that cause or allow the disease to be transmitted.
Understanding the relation between a disease and the agent causing the
disease is one of the most complex problems facing epidemiologists.
Mode of transmission is an important component of agent-disease
relationship. How does the agent infect the host and what effect does the
environment have on this relation.
Contact can be either Direct or
Indirect.
Environment for hepatitis A: the disease is transmitted through fecooral mode Contaminated water, food, Improper hygienic practices
Most setting at risk
Schools
Nursery
Restaurants
Mode of transmission:
Eat food prepared by someone who does not wash his or her hands well
after using the bathroom or changing a diaper.
Don't wash your hands after changing a diaper.
Eat raw or undercooked shellfish that was harvested from waters
contaminated with raw sewage.
Homosexual /Man has sex with men
Direct contact with infected people
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The table show the relationship between host, agent and environment characteristics and those
related to hepatitis A in red
Host
Age
Sex
Race
Religion
Customs
Occupation
Genetic profile
Marital status
Immune status
Vaccination status
Agent
Biologic
(bacteria,
viruses, toxin)
Chemical (nerve, blister)
Nuclear
Bombs and flammables
Environment
Temperature
Humidity
Altitude
Wind
Crowding
Poor
sanitation
contaminated water, food
Improper
hygienic
practices
Homosexual/
Note: Prevention measures targeting any of these three
elements; host, agent and environment
Epidemics arise when, host, agent environment factors are not in
balance due to
 New agent (avian influenza)
 Changes
in
existing
agent
(infectivity,
pathoginity,
virulence)resistance of bacteria causing influenza to antibiotics
 Changes in number of susceptible in the population
 Environmental changes affect transmission of agent or growth of
the agent ; increase in temperature and humidity are suitable
environment for Malaria agent
II.
Chain of causation in infectious disease
Epidemiologist used Chain of causation to explain the conditions
developed and offer effective prevention and protection.
The chain consist of, reservoir, portal of exist, mode of transmission,
agent, portal of entry, and the host
First link : The chain begins by (reservoir) where causal agent can live
and multiply) for example in plague, the reservoir is may be other human,
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rats, and few other animals. In Malaria, the reservoirs for the parasitic
agent are the infected human.
Second link: Portal of exist:
from the reservoir, the bites of an
Anopheles mosquito provide a portal of exist for the parasite, which
spend part of its life cycle in the mosquito body
Third link :Mode of transmission: The method of transmission is the
means by which the agent goes from the source to the host. For example
(The mosquitoes are the mode of transmission)
There are four major methods of transmission:
I.
Contact transmission: the agent is spread
 Direct contact transmission takes place when organisms are
transmitted directly from the source to the susceptible host without
involving an intermediate object; this is also referred to as personto-person transmission. An example is the transmission of hepatitis
A virus from one individual to another by hand contact.
 Indirect transmission occurs when the organisms are transmitted
from a source, either animate or inanimate, to a host by means of
an inanimate object. An example is transmission of Pseudomonas
organisms from one individual to another by means of a shaving
brush.
II.
Common-vehicle transmission refers to agents transmitted by a
common inanimate vehicle, with multiple cases resulting from such
exposure. This category includes diseases in which food or water as
well as drugs and parenteral fluids are the vehicles of infection.
Examples include food-borne salmonellosis, waterborne shigellosis,
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and
bacteremia
resulting
from
use
of
intravenous
fluids
contaminated with a gram-negative organism.
III.
The third method of transmission, airborne transmission, refers to
infection spread by droplet nuclei or dust. To be truly airborne, the
particles should travel more than 3 feet through the air from the
source to the host. Droplet nuclei are the residue from the
evaporation of fluid from droplets, are light enough to be transmitted
more than 3 feet from the source, and may remain airborne for
prolonged periods. Tuberculosis is primarily an airborne disease; the
source may be a coughing patient who creates aerosols of droplet
nuclei that contain tubercle bacilli. Infectious agents may be
contained in dust particles, which may become re-suspended and
transmitted to hosts. An example occurred in an outbreak of
salmonellosis in a newborn nursery in which Salmonellacontaminated dust in a vacuum cleaner bag was re-suspended when
the equipment was used repeatedly, resulting in infections among the
newborns.
IV.
The fourth method of transmission is vector borne transmission, in
which arthropods are the vectors. Vector transmission may be
external or internal. External, or mechanical, transmission occurs
when organisms are carried mechanically on the vector (for example,
Salmonella organisms that contaminate the legs of flies). Internal
transmission occurs when the organisms are carried within the
vector. If the pathogen is not changed by its carriage within the
vector, the carriage is called harborage (as when a flea ingests plague
bacilli from an infected individual or animal and contaminates a
susceptible host when it feeds again; the organism is not changed
while in the flea). The other form of internal transmission is called
biologic. In this form, the organism is changed biologically during
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its passage through the vector (for example, malaria parasites in the
mosquito vector).
An infectious agent may be transmitted by more than one route.
For example, Salmonella may be transmitted by a common vehicle (food)
or by contact spread (human carrier). Francisella tularensis may be
transmitted by any of the four routes
Fourth link: Agent The next link in chain is the agent itself, in Malaria;
the agent is the protozoa that multiply in mosquito
Fifth link: Then the portal of entry, the bite by mosquito provides the
portal of entry into the human host. The organism may enter the host
through the skin, mucous membranes, lungs, gastrointestinal tract, or
genitourinary tract, and it may enter fetuses through the placenta
Sixth link: Host: The last link in the chain
Development of disease in a host is influenced by host defense
mechanisms in addition to other factors as sex, age…etc.
Environment have a profound influence at any point along the chain for
example Temperature can assist or inhibit multiplication of organisms at
their reservoir; air velocity can assist the airborne movement of droplet
nuclei; low humidity can damage mucous membranes; and ultraviolet
radiation can kill the microorganisms. In any investigation of disease, it is
important to evaluate the effect of environmental factors. At times,
environmental control measures are instituted more on emotional grounds
than on the basis of epidemiologic fact. It should be apparent that the
occurrence of disease results from the interaction of many factors
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Application of chain of causation using in infectious disease to
illustrate to explain spread of Malaria
Chain link
Example
Reservoir
Infected human with malaria is the
reservoir for parasitic agent
other animals as monkey
Portal of exist
Anopheles mosquito bites infected
human
Mode of transmission
Mosquito
Agent
Protozoa multiply in mesquite
Portal of entry
Anopheles
mosquito
bites
uninfected human
Host
Human
become
infected
with
Malaria
Environment
Malaria breed in hot , high humidity
environment
Application of encephalitis causing disease
The agent is encephalitis causing disease , Transmitted through the
mosquito bite, the virus survive in the body of mosquito , these infected
mosquitoes pass the virus to another bird, human , the virus usually
destroyed in the bloodstream, if survive will in the body it can infect the
membranes around the spinal cord and brain and cause encephalitis.
The highest risk group: elderly, children people with impaired immune
system
III.
Multiple Causation Model /web causation
Epidemiological studies can never prove causation; that is, it cannot
prove that a specific risk factor actually causes the disease being studied.
Epidemiological evidence can only show that this risk factor is associated
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(correlated) with a higher incidence of disease in the population exposed
to that risk factor. The higher the correlation the more certain the
association, but it cannot prove the causation. This model considers the
health status of the host and how it is impacted by human biology, life
style, environment, and socio-culture health system ….etc.
It is also called the web of causation as it attempts to identify all possible
factors /risk factors and influences on the health and illness process
Causation versus Association
Association is the a concept that helpful in determining the multiple
causality, which is mean the events that appear together rather than being
the cause by itself.
It is an identifiable relationship between an exposure and disease implies
that exposure might cause disease, and exposures associated with a
difference in disease risk are often called “risk factors”
For example, the discovery of the link between cigarette smoking and
lung cancer was based on comparisons of lung cancer rates in smokers
and non-smokers. The rates of lung cancer are much higher in smokers
than in non-smokers. Does this prove that cigarette smoking causes lung
cancer? The studies of the associated factors suggest possible causality
and points for intervention, the association among life style, behaviors,
environment and stress.
Epidemiological studies can only go to prove that an agent could have
caused, but not that it did cause an effect in any particular case:
Cause: event or condition that plays a role in producing occurrence of a
disease
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Causation - implies that there is a true mechanism that leads from
exposure to disease. Finding an association does not make it causal
Web of causation assumptions
• There is no single cause
• Causes of disease are interacting
• Illustrates the interconnectedness of possible causes
Application of web of causation for infant Mortality
Conducting Retrospective study and use the birth and death certificate,
in addition to hospital record as source of epidemiological data was
found the following factors as associated factors to infant mortality rate
Risk factors:
Immediate factors
 Low birth weight
 Prematurity
 Congenital malformation
 Birth injury and anoxia
 Sudden infant death syndrome
 Infection
 Accidents
Intermediate factors
 Prenatal care
 Parity
 Maternal age
 Marital status
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Under ling factors
 Social condition
 Economic situation and poverty
 Educational status of parents/ women
 Race and ethnicity
Diagram show the different risk factors associated with infant
mortality rate
Race / ethnicity
Maternal age
Low
birth
weight
Risk
Prematurity
Socioeconomic/ educational status
Parity
Congenital
malformation
Marital status
Birth
injuries
and
anoxia
Prenatal care
Sudden
infant
death
Infection
Infant mortality
The probability that a disease or other unfavorable health condition will
develop
The risk of developing any health problem is influenced by population
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Accide
Biological factors: genetics, physiological function, maturation
Life style: employment, consumption, leisure and activities
Environment: physical, psychological, social
Health care system: availability, accessibility and utilization and quality
of services.
Populations at risk are collection of people whom has a greater possibility
of developing a health problem than others because either to presence of
certain factors (exposure to HIV) or factors are absent (lack of child hood
immunization
Types of epidemiological study
Epidemiological studies can be divided into two basic types depending on
(a) Whether the events have already happened (retrospective) or
(b) Whether the events may happen in the future (prospective). The most
common studies are the retrospective studies which are also called casecontrol studies. A case-control study may begin when an outbreak of
disease is noted and the causes of the disease are not known, or the
disease is unusual within the population studied.
The first step in an epidemiological study is to strictly define exactly what
requirements must be met in order to classify someone as a "case." This
seems relatively easy, and often is in instances where the outcome is
either there or not there (a person is dead or alive). In other instances it
can be very difficult, particularly if the experts disagree about the
classification of the disease. This happens often with the diagnosis of
particular types of cancer. In addition, it is necessary to verify that
reported cases actually are cases, particularly when the survey relies on
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personal reports and recollections about the disease made by a variety of
individuals. The strength of an epidemiological study depends on the
number of cases and controls included in the study. The more individual
cases that are included in the study, the more likely it is that a significant
association will be found between the disease and a risk factor. Just as
important is determining what behavioral, environmental, and health
factors will actually be studied as possible risk or protective factors. If
inappropriate factors are chosen, and the real factors are missed, the study
will not provide any useful information. In such an instance, an
association may be found between an inappropriate factor and the disease
because this inappropriate factor which we will call factor 1, is associated
with another factor, factor 2, which is actually related to the disease, but
which was not studied. In such an instance, factor 1 is called a
confounding variable, because it confounds the interpretation of the
results of the study. Thus, it is very important that epidemiologist choose
the proper factors to study at the outset, and not study too many factors at
once, since the possibility of finding confounding factors increases with
the addition of more variables.
Epidemiologic Methods
Epidemiology utilizes an organized approach to problem solving by: (1)
confirming the existence of an epidemic and verifying the diagnosis; (2)
developing a case definition and collating data on cases; (3) analyzing
data by time, place, and person; (4) developing a hypothesis; (5)
conducting further studies if necessary; (6) developing and implementing
control and prevention measures; (7) preparing and distributing a public
report; and (8) evaluating control and preventive measures.
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The three major epidemiologic used methods are descriptive, analytic,
and experimental. The most used method is descriptive epidemiology.
Once the basic epidemiology of a disease has been described, specific
analytic methods can be used to study the disease further, and a specific
experimental approach can be developed to test a hypothesis.
I.
Descriptive Epidemiology
Descriptive epidemiology aims to observe and describe pattern of healthrelated condition that occurs naturally in a population.
Data that describe the occurrence of the disease are collected by various
methods from all relevant sources. The data are then collated by time,
place, and person.
Essential elements of disease we look for in descriptive epidemiology
Time: How does the pattern of this disease vary over time in this
population?
Four time trends are considered in describing the epidemiologic data.
a) The secular trend describes the occurrence of disease over a
prolonged period, usually years; it is influenced by the degree of
immunity in the population and possibly nonspecific measures
such as improved socioeconomic and nutritional levels among the
population. For example, the secular trend of tetanus in the United
States since 1920 shows a gradual and steady decline.
b) The second time trend is the periodic trend. A temporary
modification in the overall secular trend, the periodic trend may
indicate a change in the antigenic characteristics of the disease
agent. For example, the change in antigenic structure of the
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prevalent influenza A virus every 2 to 3 years results in periodic
increases in the occurrence of clinical influenza caused by lack of
natural immunity among the population. Additionally, a lowering
of the overall immunity of a population or a segment thereof
(known as herd immunity) can result in an increase in the
occurrence of the disease. This can be seen with some immunizable
diseases when periodic decreases occur in the level of
immunization in a defined population. This may then result in an
increase in the number of cases, with a subsequent rise in the
overall level of herd immunity. The number of new cases then
decreases until the herd's immunity is low enough to allow
transmission to occur again and new cases then appear.
c) The third time trend is the seasonal trend. This trend reflects
seasonal changes in disease occurrence following changes in
environmental conditions that enhance the ability of the agent to
replicate or be transmitted. For example, food-borne disease
outbreaks occur more frequently in the summer, when temperatures
favor multiplication of bacteria. This trend becomes evident when
the occurrence of salmonellosis is examined on a monthly basis .
d) The fourth time trend is the epidemic occurrence of disease. An
epidemic is a sudden increase in occurrence due to prevalent
factors that support transmission.
Place: How does the place in which the population lives affect the disease
pattern
A description of epidemiologic data by place must consider three
different sites: where the individual was when disease occurred; where
the individual was when he or she became infected from the source; and
where the source became infected with the etiologic agent. Therefore, in
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an outbreak of food poisoning, the host may become clinically ill at home
from food eaten in a restaurant. The vehicle may have been undercooked
chicken, which became infected on a poultry farm. These differences are
important to consider in attempting preventing additional cases.
Person: How do the personal characteristics of the people in the
population affect the disease pattern? All pertinent characteristics should
be noted: age, sex, occupation, personal habits, socioeconomic status,
immunization history, presence of underlying disease, and other data.
Quantification and Statistical Analysis Used in Descriptive
Epidemiology
1) Counts
The simplest measure used in epidemiology, it is necessary to determine
what the information represents before collecting data.
2) Rates
It Is Statistical measures expressing the proportion of people with a given
health problem among a population at risk. The total number of people in
the group is the denominator for the various types of rates. And those
defined as the object of study, as it is difficult to study all entire
population.
If number of deaths among children due to RTI is 30, the rate to total
population of Nablus city will differ from that to the total population of
Palestine.
Most usable rates in epidemiology are
 Prevalence rate:
refers to all of the people with a particular
health condition existing at a given point of time
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Prevalence rate = Number of persons with disease / total number in
population
Example if number of measles in elementary school is 20, the prevalence
rate of measles in the school at that time would be 20/500, 500 is the total
number of student in the school.
 Period prevalence rate: the prevalence rate over a defined period
of time.
 Incidence rate: refers to all new cases of disease or health
condition appearing during a given time. It describes a proportion
in which the number is all new cases appearing during a given
period of time, and the denominator is population at risk during the
same period
Incidence rate =number of persons developing a disease /total number at
risk
II.
Analytic Epidemiology
The second epidemiologic method is analytic epidemiology, which
analyzes disease determinants for possible causal relations. They test
hypothesis to answer specific question and can be retrospective and
prospective in design.
The two main analytic methods are the case-control (or case-comparison)
method and the cohort method.
 The case-control method starts with the effect (disease) and
retrospectively investigates the cause that led to the effect. The
case group consists of individuals with the disease; a comparison
group has members similar to those of the case group except for
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absence of the disease. These two groups are then compared to
determine differences that would explain the occurrence of the
disease. An example of a case-control study is selecting individuals
with meningococcal meningitis and a comparison group matched
for age, sex, socioeconomic status, and residence, but without the
disease, to see what factors may have influenced the occurrence in
the group that developed disease.
 The second analytic approach is the cohort method, which
prospectively studies two populations: one that has had contact
with the suspected causal factor under study and a similar group
that has had no contact with the factor. When both groups are
observed, the effect of the factor should become apparent. An
example of a cohort approach is to observe two similar groups of
people, one composed of individuals who received blood
transfusions and the other of persons who did not. The occurrence
of hepatitis prospectively in both groups permits one to make an
association between blood transfusions and hepatitis; that is, if the
transfused blood was contaminated with hepatitis B virus, the
recipient cohort should have a higher incidence of hepatitis than
the non-transfused cohort.
The case-control approach is relatively easy to conduct, can be completed
in a shorter period than the cohort approach, and is inexpensive and
reproducible; however, bias may be introduced in selecting the two
groups, it may be difficult to exclude subclinical cases from the
comparison group, and a patient's recall of past events may be faulty. The
advantages of a cohort study are the accuracy of collected data and the
ability to make a direct estimate of the disease risk resulting from factor
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contact; however, cohort studies take longer and are more expensive to
conduct.
 Another analytic method is the cross-sectional study, in which a
population is surveyed over a limited period to determine the
relationship between a disease and variables present at the same time
that may influence its occurrence.
Basic Question in Analytic Epidemiology
 Are exposure and disease linked
 Look to link exposure and disease
 What is the exposure?
 Who are the exposed?
 What are the potential health effects?
 What approach will you take to study the relationship between
exposure and effect? Is there an association between Exposure (E) &
Disease (D)?
 Hypothesis: Do persons with exposure have higher levels of disease
than persons without exposure?
 Is the association “real,” i.e. causal
III.
Experimental Epidemiology
The third epidemiologic method is the experimental approach. A
hypothesis is developed and an experimental model is constructed in
which one or more selected factors are manipulated. The effect of the
manipulation will either confirm or disprove the hypothesis. An example
is the evaluation of the effect of a new drug on a disease. A group of
people with the disease is identified, and some members are randomly
selected to receive the drug. If the only difference between the two is use
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of the drug, the clinical differences between the groups should reflect the
effectiveness of the drug.
Source of Information in Epidemiology:
I.
Existing data ; that available at national level and includes
 Vital statistics: refers to the information gathered from ongoing
registration of birth, deaths, divorces, marriages. Birth and death
certification also provide other information as birth weight, causes
of death..etc.
 Census data: main source of population statistics and is taken
every 10 years in several countries. , it can be analyzed by age,
sex, race, marital status, income and occupation. It provides the
community health nurse with specific areas that may be important
for identifying health conditions.
 Reportable disease: several countries developed regulation and
laws regarding reporting mainly the communicable and infectious
disease which was also according to WHO recommendation, this
reporting enables the health departments to take the most
appropriate and efficient actions at suitable time.
 Disease registration: health department have disease registries for
condition with major health impact as cancer registration, which
provide useful data regard incidence, prevalence rate which help in
monitoring the cancer pattern with in a community.
II.
Informal observational studies: any client group encountered by
the community health nurse can trigger such a study. For example
if nurse encounters an abused child at health clinics, a study of the
clinic’s records to screen for additional possible instances could
lead to more case findings.
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III.
Scientific studies :the third source of information in epidemiology
is the designed scientific studies , which became one of the
community health nurses role
Application of Epidemiology
(1) To study the history of disease
Studies the trends of a disease for the prediction of trend useful
information in planning for health services and public health
Community Diagnosis
What are the diseases, conditions, injuries, disorders, disabilities, defects
causing illness, health problems, or death in a community or region?
Look at risks of individuals as they affect groups or populations
 What are the risk factors, problems, behaviors that affect groups?
 Identify the problem by health screening, medical exam, disease
assessments, etc.
 Determine the causes and sources of disease
The results will be used to design a program to control, prevention, and
elimination of the causes of disease Assessment, evaluation, and research
� how well do public health and health services meet the problems and
needs of the population or group?
� Effectiveness; efficiency of a program are studied
25
Endemic: The ongoing, usual level of a disease within a given
population or geographic area
Epidemic: An outbreak of a disease in excess of the usual level of
expectancy
Pandemic: An epidemic widespread across a county possible worldwide
Outbreak:
The essential characteristics of an epidemic that it involves a temporary
increase in the incidence of a disease both in its location or in respect
of group affected.
Primary case: the first case (group of cases) arising from the introduction
of an agent into a community.
Index case: refer to initial/ primary case
Secondary case: person who acquire infection from the primary index
Incubation period: the interval between infection of an individual and the
onset of symptoms. This differs according to the organism and may vary
according to such factors as the violence of particular strain of infecting
organism, the infecting dose and susceptibility of the host
26
Application using the three level of prevention during the 4 stages of
the natural history of a disease to eradicate or reduce risk factors
The natural history of the disease
Interrelationship of
agent , host,
environmental factors
Pre pathogenesis
period
Primary
prevention
Health
Health
education protection
Reaction of the host to the stimulus
Onset
early clinical
culmination
Period of pathogenesis
Secondary
Tertiary
Prevention
prevention
Early
Treatment Rehabilitation Primary prevention
diagnosis
Health
Health
education protection
Nutrition
Immunization Screening Initiate
Reduce
Training
Immunization
counseling
program
treatment severity
of
,
health
health
services
problem
to
minimize
disability
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To help student understand risk factors
To promote behaviors to decrease exposure and susceptibility
Primary prevention
Education
Health protection
Regard
hep.A, mode
of
transmission
Risk factors
Exposure
Occupation
period
Proper
hygienic
practice
Washing
hands
Washing and
cleaning fruit
and
vegetables
Health
education to
families and
community
through mass
media
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Immunization
for high risk groups;
children
4-18
elderly people
children should be
excluded
from
school setting for
the
period
of
communicacability
Give
immunoglobulin IG
to those who may
have been in contact
with
infected
persons and to be
given with 2 weeks
of
exposure
to
prevent occurrence
of disease.
Practice of proper
hygienic practices
always either after
use of bath room,
preparing
food,
changing the infant
diaper
Boiling water before
use
Secondary prevention
Early
Treatment
diagnosis
Screening
Bed rest for
to discover week
those who are Give
a
medication
symptomatic Proper
and
may sufficient
become
mix healthy
infected so as food drink
to
initiate lots of water
treatment as Minimize
early
as activity tell
possible
return back
the
body
energy
Gradually
return back
to activity
Tertiary prevention
Rehabilitation Health
education
Psychological
Education
support
for for clients
client
and after
families
recovery
Ensure
that about the
clients
are disease
following the and risk
treatment
factors
protocol
in and
term of eating, preventive
activity …etc measures
to return back
health as soon
as possible and
to prevent any
adverse effect