EPIDEMIOLOGICAL
APPLICATIONS IN
CHN
PRESENTING BY:
DR/AMIRA YAHIA
DEFINITION OF EPIDEMIOLOGY
• Epidemiology is the study of the distribution and determinants
of health and disease in human populations, and is the
principal science of community health practice.
Cont….
• Community health nurses use epidemiological concepts to
improve the health of population groups by identifying risk
factors and optimal approaches that reduce disease risk.
• Epidemiological methods are important for accurate
community assessment and diagnosis and in planning and
evaluating effective community interventions
USES OF EPIDEMIOLOGY IN DISEASE
CONTROL AND PREVENTION
1. Identifying characteristics of people who suffered from a
disease such as cholera or plague and compared them with
characteristics of those who are healthy such as personal factors,
socioeconomic status and health status
Cont….
2. Questioning whether there were differences in the location or
living environment of ill people compared with healthy
individuals and whether these factors influenced disease
development
3. Examining whether common time factors existed (i.e., when
people acquired disease)
EPIDEMILOGICAL METHODS
1.
Descriptive epidemiology :
• Descriptive Epidemiology focuses on the amount and
distribution of health and health problems within a
population.
• Its purpose is to describe the characteristics of people who are
protected from disease and those who have a disease.
Cont….
• Factors of particular interest include age, sex, ethnicity or
race, socioeconomic status, occupation and family status.
• Epidemiologists use morbidity and mortality rates to describe
the extent of disease and to determine the risk factors that
make certain groups prone to acquiring disease.
2. Analytic Epidemiology:
• Analytic Epidemiology investigates the causes of disease by
determining why a disease rate is lower in one population group
than in another.
• This method tests hypothesis generated from descriptive data and
either accepts or rejects them on the basis of analytic research.
• The epidemiologist seeks to establish a cause and effect
relationship between preexisting condition or event and the
disease.
EPIDEMIOLOGICAL TRIANGLE
MODEL
• Is the examination of the interrelationships between host and
environmental characteristics and uses an organized method
of injury to derive an explanation of disease. In this model the
epidemiologist must analyse the following three elements:
agent, host and environment
Cont…..
• The development of disease is dependent upon:
a. The strength of the agent
b. The host’s genetic or immunological susceptibility
c. The environmental conditions existing at the time of exposure,
which includes the biological, social, political and physical
environment.
Cont…..
• The model implies that the rate of disease will change when
the balance among these three factors is altered.
• By examining each of the three elements, a community health
nurse can methodically assess a health problem, determine
protective factors and evaluate the factors that make the host
vulnerable to disease.
Host
Environment
Agent
Epidemiological Triangle
Cont….
• In studying chronic diseases, epidemiologists use methods
that are similar to those used in infectious disease
investigation, thereby developing theories about chronic
disease control. Risk factor identification is of particular
importance to chronic disease reduction
RISK FACTORS
• Risk factors variables that increase the rate of disease in
people who have them (e.g., a genetic predisposition) or in
those exposed to them (e.g., an infectious agent or a diet high
in saturated fat). Therefore their identification is critical to
identifying specific prevention and intervention approaches
that effectively and efficiently reduces chronic disease
morbidity and mortality.
Cont….
• For example, the identification of cardiovascular disease risk
factors has suggested a number of lifestyle modifications that
could reduce the morbidity risk before disease onset. Primary
prevention strategies such as dietary saturated fat reduction,
smoking cessation and hypertension control developed in
response to previous epidemiological studies that identified
these risk factors.
CALCULATION OF RATES
• The community health nurse must analyze data about the
health of the community determine the pattern of disease in a
community.
• The nurse may collect data by conducting surveys or compiling
data from existing records (e.g., data from clinic facilities or
vital statistics records).
• Often assessment data are in the form of counts or simple
frequencies of events (e.g., the number of people with a
specific health condition).
• Community health nurse interpret these raw counts by
transforming them into rates.
RATES:
• Rates are arithmetic expressions that help nurses consider a
count of an event relative to the size of the population from
which it is extracted (e.g., the population at risk).
• When raw counts are converted to rates, the community
health nurse can make meaningful comparisons with rates
from other countries, from the nation and from previous time
periods.
Cont….
• These analyses assist the nurse in determining the magnitude
of a public health problem in a given area and allow more
reliable tracking of trends in the community over time
MORBIDITY RATES OF ILLNESS
1. Incidence Rate
• Incidence rates describe the occurrence of new cases of a
disease or condition (e.g., teen pregnancy) in a community
over a period of time relative to the size of the population at
risk for that disease or condition during that same time
period.
• The incidence rate may be the most sensitive indicator of the
changing health of a community because it captures the
fluctuations of disease in a population
2. Prevalence Rate
• Is the number of all cases of a specific disease or condition (e.g.,
deafness) in a population at a given point in time relative to the
population at the same point in time.
• Morbidity rates are not available for many conditions because
surveillance of many chronic diseases is not widely conducted.
Furthermore, morbidity rates may be subject to underreporting
when they are available. Routinely collected birth and death rates,
or mortality rates, are more widely available.
OTHER RATES
1. Crude rates (Basic, rough Rates)
• Summarize the occurrence of births (i.e., crude birth rate),
mortality (i.e., crude death rates), or diseases (i.e. crude
disease rates), in the general population.
• Age specific rates characterize a particular age group in the
population and usually consider deaths and births.
Determining the rate for specific subgroups of a population
and using a denominator that reflects only that subgroup
removes age bias.
a. Crude birth rate = number of live births during the year/average
(midyear) population Per 1000 population
b. Crude death rate = number of deaths during the year/average
(midyear) population Per 1000 population
c. Age-specific death rate = number of deaths among people of a
given age group in one year/average (midyear) population in specified
age group Per 1000 population
d. Cause-specific death rate = number of deaths from a stated cause in
one year/average (midyear) population Per 100,000 population
USE OF EPIDEMIOLOGY IN DISEASE
PREVENTION
1. Primary Prevention
The central goals of epidemiology are:
a. Describing the disease patterns
b. Identifying the etiologic factors in disease development
c. Finding the most effective preventive measures.
• When these measures occur before disease development, they are
called primary prevention.
• Primary prevention relies on epidemiological information to
indicate those behaviors that are protective, or will not contribute
to an increase in disease, and those that are associated with
increased risk.
2. Secondary and Tertiary Prevention
• Secondary prevention occurs after pathogenesis.
• Those measures designed to detect disease at its earliest stage,
namely screening and physical examinations that are aimed at
early diagnosis, are secondary prevention.
• Interventions that provide for early treatment and cure of disease
are also in this category.
• Tertiary prevention includes the limitation of disability and the
rehabilitation of those with irreversible disease such as diabetes
and spinal cord injury.
ESTABLISHING CAUSALITY
• A principal goal of classic epidemiology is to identify etiologic
factors of diseases to encourage the most effective primary
prevention activities.
• The following six criteria establish the existence of a cause and
effect relationship:
Cont…
1. Strength of association: Rates of morbidity or mortality must
be higher in the exposed group than in the non-exposed group.
Relative risk ratios or odds ratios, and correlation coefficients
indicate whether the relationship between the exposure variable
and the outcome is causal.
Cont…
• For example, epidemiological studies demonstrated an
elevated relative risk for heart disease among smokers
compared with nonsmokers.
2. Dose-response relationship: An increased exposure to the risk
factor causes a concomitant increase in disease rate.
The risk of heart disease mortality is higher for heavy smokers
compared with light smokers.
3. Temporally correct relationship: Exposure to the causal factor
must occur before the effect or disease. For heart disease, smoking
history must precede disease development
4. Biological plausibility: The data must make biological sense and
represent a coherent explanation for the relationship. Nicotine and
other tobacco-derived chemicals are toxic to the vascular
endothelium. In addition to raising low-density lipoprotein (LDL) and
decreasing high-density lipoprotein (HDL) cholesterol levels,
cigarette smoking causes arterial vasoconstriction and platelet
reactivity, which contributes to platelet thrombus formation
5. Consistency with other studies: Varying types of studies in
other populations must observe similar associations. Numerous
studies of different designs have repeatedly supported the
relationship between smoking and heart disease.
6. Specificity: The exposure variable must be necessary and
sufficient to cause disease; there is only one causal evidence, this
criterion is
less important today. Diseases do not have single causes; they
have multi-factorial origins.
SCREENING
• The purpose of screening programs is to identify risk factors
and diseases in their earliest stages.
• Screening is usually a secondary prevention activity because
disease appears after a pathological change has occurred or
ideally, early in the disease process.
SURVEILLANCE
• In addition to screening, surveillance is a mechanism for the
ongoing collection of community health information.
Monitoring for changes in disease frequency is essential to
effective and responsive public health programs.
Cont….
• Identifying trends in disease incidence or identifying risk factor
status by location and population subgroup over time allows
the community health nurse to evaluate the effectiveness of
existing programs and implement interventions targeted to
high-risk groups.
Thanks