Epidemiology

PRESENTED BY,
MR. KAILASH NAGAR
ASSIST. PROF.
DEPT. OF COMMUNITY HEALTH NSG.
DINSHA PATEL COLLEGE OF NURSING, NADIAD

Definitions
 Health: Health is a state of complete physical,
mental and social wellbeing of a person and
not merely absence of disease or infirmity
 Epidemiology: The study of distribution and
determinants of health- related states or
events in specified populations, and the
application of this study to the control of
health problems

History of Epidemiology
 Epidemiology is derived from the word epidemic( epi= among, demos=
people, logos= study) which dates back to 3rd century B.C.
 The foundation was laid in 19th century when a few classic studies made a
major contribution to saving life
 Epidemiological society in London in 1850 under the presidency of Earl of
Shaftsbury did investigations of infectious diseases
 The growth of bacteriology took epidemiology to universities
 Early 1920s: Winslow and Sedgwick both lectured in epidemiology but the
subject did not get departmental status
 1927: W.H.Frost became the first professor of epidemiology and medical
statistics in University of London

History of Epidemiology
 Dr. John Snow is famous for his investigations into the causes
of the 19th Century Cholera epidemics. He began with noticing
the significantly higher death rates in two areas supplied by
Southwark Company. His identification of the Broad Street
pump as the cause of the Soho epidemic is considered the
classic example of epidemiology. He used chlorine in an
attempt to clean the water and had the handle removed, thus
ending the outbreak. This has been perceived as a major event
in the history of public health and can be regarded as the
founding event of the science of epidemiology
 Another important pioneer was Hungarian physician who in
1847 brought down infant mortality at a Vienna hospital by
instituting a disinfection procedure. His findings were
published in 1850, but his work was ill received by his
colleagues, who discontinued the procedure. Disinfection did
not become widely practiced until British surgeon Joseph Lister
'discovered' antiseptics in 1865 in light of the work of Louis
Pasteur

Scope of Epidemiology
 Its not just concerned with death illness and disability but also with
positive health states with means to improve health
 The target study is usually human population
 Early studies of epidemiology were concerned with the causes of
communicable diseases, in this sense epidemiology is a basic medical
science with the goal of improving health of the population
 Epidemiology is increasingly used to study the influence and preventive
intervention of behavior and lifestyle through health promotions
 It is also concerned with course and outcome of disease in individual
groups. It lends a strong support to both preventive and clinical medicine
 It is often used to describe health status of the population group
 Recently it has been used for evaluating efficiency and efficacy of health
care services

Aims of Epidemiology
 According to International Epidemiological Association (IEA)
epidemiology has three main aims
 To describe the distribution and magnitude of health and disease
problems in human population
 To identify etiological factors (risk factors) in the pathogenesis of
disease
 To provide the data essential to the planning, implementation and
evaluation of services for the prevention, control and treatment and to
the setting up of priorities among those services
 The ultimate aim of epidemiology is to lead to effective
action:
 To eliminate or reduce the health problems or its consequences
 To promote the health and well being of society as a whole

Epidemiological Approach
 The epidemiological approach to problems of
health and disease is based on two major
foundations:
 Asking Questions
 Making comparisons

Asking Questions
 Epidemiology has been defined as a means of
learning or asking questions….and getting answers
that lead to more questions. For example
 Questions asked related to health events
 What is the event? (problem)
 What is the magnitude?
 Where did it happen?
 When did it happen?
 Who are affected?
 Why did it happen?

Asking questions……
 Related to health action
 What can be done to reduce problem and its
consequences?
 How can it be prevented in future?
 What action should be taken by the community?
By the health services? By other sectors? Where
and for whom these activities be carried out ?
 What difficulties may arise and how might they be
overcome?

Making Comparisons
 Basic approach to epidemiology is to make
comparisons and draw inferences
 Comparison of two or more groups: One group
having disease or exposed to the risk factor and the
other group (s) not having disease or not exposed to
the risk factor, or comparison between individuals.
 Epidemiologist tries to find out the crucial
differences in the host and environmental factors
between those affected and not affected

Uses of Epidemiology
 The study of disease distribution and causation remain central
to epidemiology but the techniques of epidemiology have a
wider application covering many more important areas
relating not only to disease but to health and health services
 Morris has identified 7 distinct uses of epidemiology
 To study historically the rise and fall of disease in a population
 Community diagnosis
 Planning and evaluation
 Evaluation of individual’s risk and chances
 Syndrome identification
 Completing the natural history of disease
 Searching for cause and risk factors

To study the historical rise and fall of disease
in a population
 To study history of a disease in a human population.
The health and disease pattern never remain
constant in a community
 Epidemiology provides means to study disease
profiles and time trends in human population
 The study of these trends will enable us to make
useful predictions in the future and identify
emerging health problems and their correlates

Community Diagnosis
 Identification and quantification of health problem in a community in
terms of mortality and morbidity, rates and ratios and identification of
their correlates for the purpose of defining those individuals or population
at risk or those in need of health care
 Quantification:
 Lay down priorities in disease control
 Using morbidity and mortality data to evaluate the efficiency of health care
services at a later date
 The quantification of health problem can be source of new knowledge about
disease distribution, causation and prevention
 Community diagnosis has gone even beyond to include and understanding
of social cultural and environmental characteristics of the community.
 Epidemiology is defined as diagnostic tool for community Medicine

Planning and Evaluation
 Planning: Epidemiological information about distribution of
health problems over time and place provides fundamental
basis for planning and developing the needed health services
and for assessing the impact of these services on people’s
problem
 Evaluation: Any measures taken to prevent or control must be
followed by an evaluation too find out whether the measures
undertaken are effective in reducing the frequency of disease.
Its not enough to just find out if the programme was effective
or not but epidemiology helps to know how much benefit at
what cost and risks.

Evaluation of individual risk and Chances
 One of the most important task for an
epidemiologist is to make a statement about
the degree of risk in the population
 An epidemiologist calculates various measures
like absolute risk, relative risk and attributable
risk for a factor related to or believed to be a
cause of the disease

Syndrome Identification
 Medical syndromes are identified by observing
frequently associated findings in individual
patients
 Epidemiological methods can be used to
define and refine syndromes

Contemplating Natural History of Diseases
 Epidemiology is concerned with the entire spectrum
of disease in a population
 The epidemiologist by studying the disease pattern in
the community in relation to agent host and
environmental factors is in a better position to fill up
the gaps in the natural history of the disease
 Epidemiological studies have yielded a large amount
of data on risk factors in relation to chronic diseases

Searching for Cause and Risk Factors
 Epidemiology by relating disease to inter population
differences and other attributes of the population or
cohorts examined, tries to identify the cause of the
disease
 The concept of risk factor gave a renewed impetus to
epidemiological research
 It is a ceaseless effort as our ignorance about the
disease etiology particularly chronic disease, is
profound and the ever emergence of new diseases

Concepts of causation of disease
and their screening

Concept of Disease
•
A pathological condition of a part, organ, or
system of an organism resulting from various
causes, such as infection, genetic defect, or
environmental stress, and characterized by an
identifiable group of signs or symptoms

The Concept of Cause
 The cause of a disease is an event, condition,
characteristic or combination of these factors which
play an important role in producing the disease
 A cause is termed sufficient when it inevitably
produces or initiates disease and is termed necessary
if a disease cannot develop in its absence
 It usually not a single factor but often comprises of
several components

Causation of Disease
 Temporal Relationship: The cause must precede the effect
 Plausibility: An association is plausible and thus more likely to
be causal if consistent with other knowledge
 Consistency: It is demonstrated by several studies giving the
same result. It is particularly important when a variety of
designs are used in different settings, since the likelihood that
all studies are making same mistake is thereby minimized.
However the lack of consistency does not exclude a causal
association
 Strength: A strong association between possible cause and
effect, as measured by the size of the risk ratio is more likely
to be causal then a weak association. Relative risk greater
than 2 is considered to be strong

Causation of disease
 Dose Response relationship: It occurs when changes in the
level of possible cause are associated with changes in the
prevalence or incidence of the effect. The demonstration of a
clear dose- response relationship in unbiased studies provides
strong evidence for a causal relationship between exposure or
dose
 Reversibility: When the removal of a possible cause results in
reduced disease risk, the likelihood of association being causal
is strengthened
 Study Design: The ability of a study design to prove causation
is a most important consideration. The best design comes
from a well designed, competently conducted randomized
controlled trails

Judging the evidence
 There is no reliable criteria for judging if the
association is causal or not. Causal
interference is usually tentative and
judgments must be made on the basis of the
available evidence; uncertainty always
remains.
 Evidence is often conflicting and due weight
must be given to different types when
decisions are being made

Causation of Disease
• In judging different aspects of causation referred to
above, correct temporal relationship is essential;
once that has been established the greatest weight
must be given to plausibility, consistency and the
dose response relationship. The likelihood of causal
relationship is heightened when many different types
of evidence lead to the same conclusion. Evidence
from well designed studies is particularly important if
they are conducted in a variety of locations.

Temporal relation Does the cause precede the effect? (essential)
Plausibility Is the association consistent with other knowledge?
(mechanism of action ; evidence from experimental
animals)
Consistency Have similar results been shown in other studies?
Strength What is the strength of association between the
cause and the effect?
Dose response
relationship
Is the increased exposure to possible cause
associated with increased effect?
Reversibility Does the removal of the possible cause lead to
reduction of disease risk?
Study Design Is the evidence based on strong study design?
Judging the
Evidence
How many lines of evidence leads to conclusion?

Concept of causation
 Germ theory of disease:
Disease agent→ Man → Disease
 Multifactorial causation: factors like socioeconomic,
cultural, genetic and psychological
 Web of causation (chronic diseases): it considers all
the predisposing factors of any type and their
interrelationship with each other

Natural history of disease
 It signifies the way in which a disease evolves
over time from earliest stage of its
prepathogenesis to its termination as
recovery, disability or death, in the absence of
treatment or prevention
 Phases of natural history of disease
 Prepathogenesis ( process in the environment)
 Pathogenesis( Process in man)

Natural history of disease contd..
 Prepathogenesis phase: The
interaction of agent host and
environment to initiate the
disease process in man
 Pathogenesis Phase: Begins
with the entry of agent in
susceptible host and ends
with recovery, disability or
death

Agent Factors
 A substance living or non living, or a force tangible or
intangible, the excessive presence or relative lack of
which may initiate or perpetuate a disease process
 Biological agents: viruses, bacteria, fungi, protozoa etc
 Nutrient agents: proteins, vitamins, fats etc
 Physical agents: heat cold
 Chemical agents: Endogenous or Exogenous
 Mechanical agents
 Social agents
 Absence, insufficiency or excess of a factor necessary for
health

Iceberg phenomenon of disease
 Epidemiologists and others who study disease
find that the pattern of disease in hospitals is
quiet different from that in the community. A
far larger proportion of disease is hidden form
view in the community then is evident to the
physician or the general public.

Concept of screening
• It is defined as “The search for unrecognized
disease or defect by means of rapidly applied
tests, examinations or other procedures in
apparently healthy individuals.”

Difference between Screening and periodic
health examinations
 Capable of wide application
 Relatively inexpensive
 Requires little physician time, in fact the
physician is not required to administer the test
but only to interpret it.

Screening and Diagnostic test
Screening Diagnostic test
Done on apparently healthy Done on those with indications or sick
Applied to groups Applied to single patient’s all diseases concerned
Test results are arbitrary and final Diagnosis is not final but modified in the light of
new evidence, diagnosis is the sum of all
evidences
Based on one criterion or cut off
point
Based on evaluation of a number of symptoms,
signs and laboratory findings
Less accurate More Accurate
Less Expensive More expensive
Not a bias for treatment Used as a bias for treatment
The initiative comes from the
investigator or agency providing
care
The initiative comes from a patient with a complaint

Aims and objectives
 The basic purpose of
screening is to sort out
of large group of
apparently healthy
persons those likely to
have disease or at
increased risk of the
disease under study, to
bring those who are
“apparently abnormal”
under medical
supervision and
treatment
Apparently
Healthy
Apparently
normal
(Periodic
Screening)
Apparently
Abnormal
Normal-
Periodic
rescreening
Intermediate-
Surveillance
Abnormal-
Treatment

Uses of Screening
 Four Main uses
 Case Detection
 Control of Disease
 Research purposes
 Education opportunities

Uses of Screening
 Case Detection:
 Also known as prescriptive screening
 It is defined as the presumptive identification of
unrecognized disease which does not arise from a
patient’s request
 Since disease detection is initiated by medical and
public health personnel, they are under the
special obligation to make sure that appropriate
treatment is started early

Uses of Screening
 Control of Disease:
 Also known as prospective screening.
 People are examined for benefit of others e.g.
screening of immigrants form infectious diseases
such as TB and syphilis to protect the home
population
 The screening programme may by leading to early
diagnosis permit more effective treatment and
reduce the spread of infectious disease and/or
mortality from the disease

Uses of Screening
 Research Purposes
 Screening may aid at obtaining more basic knowledge about
the natural history of such diseases, e.g., initial screening
provides a prevalence estimate and subsequent screening
provides incidence figure
 When screening is done for research purpose the investigator
should inform the participant that no follow-up therapy will
be available
 Educational opportunities: Screening programmes
provide opportunities for creating public awareness
and for educating health professionals

Types of Screening
• Three types of screening:
 Mass Screening
 High Risk or Selective Screening
 Multiphasic Screening

Mass Screening
 Screening of a whole population or sub group
 It is offered to all irrespective of particular risk
individual may run of contracting the disease in
question
 However indiscriminate mass screening is not a
useful preventive measure unless it is backed by
suitable treatment that will reduce the duration of
illness or alter its final outcome

High Risk or Selective Screening
 Screening will be most productive if applied
selectively to high risk groups, the groups defined on
the basis of epidemiological research
 One population subgroup where certain diseases
tend to aggregate is the family, thus by screening
other members of the family the physician can
detect additional cases
 Screening for risk factors as recent concept
 Economic use of resources

Multiphasic Screening
 Application of two or more screening tests in
combination to a large number of people at one time
then to carry out screening tests for a single disease
 Health questionnaire, Clinical examination and a
range of measurements and investigations all of
which is performed with the appropriate staffing
organization and equipment
 Added to the cost of health care services without any
observable benefit

Criteria for Screening
 Before a screening programme is initiated, a
decision should be made whether it is
worthwhile, which requires ethical, scientific
and if possible financial justification.
 The criteria is based o two things
 Disease to be screened
 Test to be applied

Disease to be Screened
 The condition sought should be an important health problem
 There should be a recognizable latent or early asymptomatic stage
 The natural history of condition including development from latent to
declared disease should be adequately understood
 There is a test that can detect the disease prior to the onset of signs and
symptoms
 Facilities should be available for the confirmation if diagnosis
 There is an effective treatment
 There should be and agreed- on policy concerning whom to treat as
patients
 There is good evidence that early detection and treatment reduces
morbidity and mortality
 The expected benefits of early detection exceed the risks and costs

Test to be applied
 Acceptability: The test should be acceptable to
people it is aimed. The tests are usually
painful, discomforting or embarrassing and
are not likely to be acceptable to the
population in mass campaigns

Repeatability
 An attribute of an ideal screening test is that
the test must give consistent results when
repeated more than once on a same individual
or material under similar conditions
 It depends on three factors
 Observer variation
 Biological variation
 Errors relating to technical methods

Observer variation
 Intra – observer variation: If a single observer takes
two measurements in the same subject at the same
time and each time he obtained a different result. It
may be minimized by taking the average of special
replicate measurements at the same time
 Inter- observer variation: The variation between
different observers on the same subject or material,
also known as between observer variation

Biological Variation
 There is biological variability associated with
many psychological variables such as BP, BS,
Sr. Cholesterol
 The change may be due to
 Changes in the parameters observed
 Variations in way patients perceive their
symptoms and answer
 Regression to the mean

Errors relating to technical methods
 Repeatability may be affected variations
inherent in the method, e.g. defective
instrument, erroneous calibration, faulty
reagents, or the test itself might be
inappropriate.
 Larger the errors lesser the repeatability and a
single test result will be unreliable

Validity (Accuracy)
 The ability of a test to separate or distinguish
those who have the disease from those who
do not
 It has two components
 Sensitivity
 Specificity

Evaluation of screening tests
 Sensitivity= a/(a+c) X 100
 Specificity= d/ (b+d) X 100
 Predictive value of positive
test= a/(a+b) X 100
 Predictive value of negative
test= d/ (c+d) X 100
 Percentage of false negatives=
c/ (a+c) X 100
 Percentage of false positive=
b/ (b+d) X 100
Screeni
ng test
results
Diagnosis Total
Diseased Not
diseased
Positive a (true
positive)
b ( False
positive)
a+b
Negativ
e
c (false
negative)
d (true
negative)
c+d
Total a+ c b+d a+b+c+
d

Sensitivity and Specificity
 Sensitivity
 Statistical index for accuracy
 The ability of a test to identify correctly all those who have
disease, that is true positive
 90% sensitivity means??
 Specificity
 The ability of a test to identify correctly all those who do not
have the disease, that is true negative
 90% specificity means??

Predictive Accuracy
• The performance of a screening test is measured by
its predictive accuracy which reflects diagnostic power
of the test
• It depends upon sensitivity, specificity and prevalence
of the disease
• The predictive value of a positive test indicates the
probability that a patient with positive test result has in
fact the disease in question
• The more prevalent the disease is the The predictive
value of a positive screening falls as disease
prevalence declines

Evaluation of Screening programmes
 Randomized controlled trials:
 Ideally evaluation should be done by randomized
controlled trail in which one group receives the
screening test, and a control which receives no
such test
 Ideally RCT should be performed in the setting
where
 Uncontrolled Trials:
 Other Methods:

Prevention of disease/s
 Successful prevention of disease depends on
knowledge of causation, dynamics of
transmission, identification of risk factors and
risk groups, availability of prophylactic or early
detection and treatment measures
 Levels of prevention
 Primordial prevention
 Primary prevention
 Secondary prevention
 Tertiary prevention

Prevention contd…..
 Primordial prevention: Prevention of emergence or
development of risk factors in countries or
population groups in which they have not yet
appeared. The main intervention being through
individual and mass education
 Primary prevention: action taken prior to onset of
disease. It signifies intervention in the
prepathogenesis phase of disease.
 Population ( Mass ) strategy: Directed to whole population
irrespective of individual risk levels
 High- risk strategy: Bringing preventive care to individuals at
high risk

Prevention contd…
 Secondary prevention: The action that halts the
progress of disease at its incipient stage and prevents
complications. Interventions: early diagnosis and
adequate treatment
 A domain of clinical medicine
 Perfect tool for controlling transmission of diseases
 More expensive and less effective then primary prevention
 Tertiary prevention:
 Intervention in the late pathogenesis phase
 All measures available to reduce or limit impairments and
disabilities, minimize the suffering caused by existing
departures from good health and to promote patients
adjustment to the irremediable condition

Basic Measurements of
Epidemiology

Basic measurements in Epidemiology
 Epidemiology focuses on measuring Mortality and
Morbidity among other things
 The first thing is to establishment of criteria and
standards by which it can be measured (goal of
epidemiology)
 Unlike a clinician an epidemiologist requires a precise
definition which is
 Acceptable and applicable to its use in large population
 Precise and valid, to enable him to identify those who have
disease from those who do not

Measurements in Epidemiology
 The scope of measurements in epidemiology is broad and
unlimited and includes
 Measurement of Morbidity
 Measurement of Mortality
 Measurement of disability
 Measurement of Natality
 Measurement of the presence, absence or distribution of the
characteristics or attributes of the disease
 Measurement of presence, absence or distribution of the
environmental and other factors suspected of causing the disease
 Measurement of demographic variables
 The basic requirements of measurements are validity,
reliability, accuracy, sensitivity and specificity

Tools of Measurement
 Rates:
 A rate measures the occurrence of some particular event in a
population during a given time period e.g Death Rate
 Crude rates: these are the actual observed rates such as birth and
death rates (usually expressed per 1000)
 Specific rates: These are the actual observed rates due to specific
causes or occurring in specific groups or during specific time periods
 Standardized rates: These are observed by direct or indirect method of
standardization or adjustment, e.g age and sex standardized rates
 Ratios:
 It expresses a relation in size between two random quantities
 Proportion:
 It is a ration which indicates the relation in magnitude of a part of the
whole (usually expressed as percentage)

Measurement of Mortality
 Most epidemiological studies begin with mortality data
 Easy to obtain and in most of the countries very accurate
 International Death Certificate:
 It was recommended by WHO for international use, for ensuring
national and international comparability
 It is divided in two parts: the first part includes immediate cause and
underlying cause which started the whole events leading to death
 The “underlying cause” is the essence of international death
certificate and is defined as
 The disease or injury that started the train of morbid events leading
directly to death
 The circumstances of accident of violence which produced the fatal injury
 The second part records any significant associated diseases that
contributed to death but did not directly lead to it
 Death certificate used in India

Uses and Limitations of Mortality Data
 Uses:
 Explaining trends and differentials in overall mortality, indicating
priorities for health actions and allocation of resources
 Designing intervention programmes
 Assessing and monitoring of public health problems and programmes
 Important clues for epidemiological research
 Limitation
 Incomplete reporting of deaths: Developing countries
 Lack of accuracy: age and cause of death
 Lack of uniformity: no uniform method
 Choosing a single cause of death: underlying cause, risk factor
 Changing
 Diseases with low fatality: mental diseases, arthritis

Crude Death Rate
 Number of deaths (from all causes) per 1000
estimated mid year population in one year in a given
place
Number of deaths during the year
X 1000
Mid year population
 The major disadvantage with crude death rate is that
they lack comparability for communities with
populations that differ in age, sex, race etc

• Specific death rates
 The specific death rates may be
 Cause or disease specific e.g., Tuberculosis
 Related to specific groups e.g., age specific, sex- specific
Case Fatality Rate (Ratio)
Total number of deaths due to a particular disease X 100
Total number of cases due to the same disease
 It represents the killing power of the disease and its use for
chronic diseases is limited because the period from onset to
death is long and variable
 It is closely related to virulence

 Proportional Mortality Rate
 Proportion of total deaths due to a particular cause (deaths in a specific age
group) per 100 (or 1000) total deaths
 Proportional mortality rate from a specific disease:
Number of deaths from a specific disease in a year
Total deaths from all causes in a year
 It is usually computed for a broad disease group or a specific disease of
major public health importance, such as cancer, coronary heart disease
 It is of little importance for making comparisons between population
groups or different time periods since it depends on two variable and both
of which may differ
 It is however important indicator within any population group of relative
importance of the specific disease or disease group as a cause of death
 Mortality

Survival Rate
• It is a method of describing prognosis in
certain disease conditions from date of
diagnosis or start of treatment. Special
interest in cancer studies
• Total number of patients alive after 5 years X 100
• Total number of patients diagnosed or treated

Adjusted or Standardized Rates
 The rates are comparable only if the populations on
which they are based is comparable, thus crude rate
is not always useful
 Two types of Standardization
 Direct Standardization
 Indirect Standardization
 Standard Population is defined as one for which the
numbers each sex and age are known

Direct Standardization
 Apply to the standard population the age specific
rates of the population whose crude death rate to be
adjusted or standardized
 As a result for each age group a expected number of
deaths in the standard population is obtained; this is
added together for all the age groups to give the
total expected deaths
 Divide the expected total number of deaths by the
total of the standard population which yields the
standardized or age adjusted rate

Example
• Calculating age specific death rates for City X
Age Mid year population
per 1000
Deaths in the year Age specific death
rates
0 4,000 60 15.0
1-4 4,500 20 4.4
5-14 4,000 12 3.0
15-19 5,000 15 3.0
20-24 4,000 16 4.0
25-34 8,000 25 3.1
35-44 9,000 48 5.3
45-54 8,000 100 12.5
55-64 7,000 150 21.4
53,500 446
Crude death rate per 1000 = 8.3

Example
• Calculating age standardized death rates for City X
Age Standard population Age specific death
rates
Expected deaths
0 2,400 15.0 36
1-4 9,600 4.4 42.24
5-14 19,000 3.0 57
15-19 9,000 3.0 27
20-24 8,000 4.0 32
25-34 14,000 3.1 43.4
35-44 12,000 5.3 63.6
45-54 11,000 12.5 137.5
55-64 8,000 21.4 171.2
93,000 609.94
Standardized death rate per 1000= (609.94/ 93,000)* 1000 = 6.56

Indirect age standardization
 Standardized mortality Ratio
Observed deaths X 100
Expected Deaths
 More stable rates of the larger population are
applied to smaller study group
 IT gives a measure of the likely excess risk of
mortality due to the occupation
 Advantage over Direct method: it permits
adjustment for age and other factors where age
specific rates are not available or are unstable
because of small numbers

Morbidity
 Morbidity is defined as any departure,
subjective or objective from the state of
physiological wellbeing
 Morbidity can be measured in terms of 3 units
 Person who were ill
 The illness periods that the person has
experienced
 The duration of these illnesses

The value of Morbidity Data
 They describe the extent and nature of the disease load in the
community and thus assist in the establishment of priorities
 They usually provide more comprehensive and more accurate
and clinically relevant information on patient characteristics
than can me obtained from mortality data and are therefore
essential for basic research
 They serve as starting point for etiological studies and thus
play a crucial role in disease prevention
 They are needed for monitoring and evaluation of diseases
control activities

Incidence
 It is defined as number of new cases occurring
in a defined population during a specified
period of time
Number of new cases of specific disease
during and given time period X 1000
Population at risk during that period

Incidence rate refers
 Only to new cases
 During an gives period
 In a specified population or population at risk
unless other denominators are chosen
 It can also refer to new spells or episodes
arising in a given period of time, per 1000
population

Attack Rate
 It is type of incidence rate used only when the
population is exposed to risk for a limited
period of time such as during an epidemic
Number of new cases of a specified disease
during a specified time interval X100
Total population at risk during
the same interval

Secondary Attack rate
 It is defined as the number of exposed
persons developing the disease within the
range of incubation period following the
exposure to a primary case

Uses of Incidence Rate
 It is useful for taking action as a health status
indicator
 To control the disease
 For research into etiology and pathogenesis of
disease, distribution of diseases, and efficacy of
preventive and therapeutic measures

Prevalence
 The total number of all individuals who have
an attributable or disease at a particular time
(or during a particular period) divided by the
population at risk of having attribute or
disease at this point of time or midway
through the period
 Types of prevalence
 Point prevalence
 Period prevalence

Point Prevalence
 The number of all current cases (old and new)
of a disease at one point in time in relation to
a defined population
No. of all current cases of a specified disease
existing at a given point of time X 100
Estimated population at the same time

Period Prevalence
 It is the less commonly used kind of prevalence
 The number of all current cases (old and new) of a
disease during a defined period of time expressed in
relation to a defined population
No. of all current cases of a specified disease
existing at a given period of time interval X 100
Estimated mid interval population at risk

Uses and Limitations of Prevalence
• Uses
 Prevalence helps to estimate the magnitude of
health/ disease problems in the community and
identify potential high risk populations
 Prevalence rates are especially useful for
administrative and planning purposes
Limitation
 It is not the ideal measure for studying disease
etiology or causation

Relationship between Incidence and Prevalence
 Prevalence depends on two factors Incidence and
Duration of illness
P = I x D
 The longer the duration of disease the greater is the
prevalence
 At the same time if the duration of disease is low due
to death or recovery then the prevalence rates will
be relatively low as compared to incidence

Surveillance
 It is an essential part of disease control.
 There are various ways of undertaking surveillance most important being
reporting the cases within health system. It requires continuous scrutiny
of all aspects of occurrence, spread and control of disease that are
pertinent to effective control. The analysis of data from a surveillance
system indicates whether there has been a significant increase in the
number of cases
 Sentinel Health information system: a limited number of general
practitioners report on a defined list of carefully chosen topics that may be
changed from time to time are increasingly used to provide
supplementary information for surveillance of both communicable and
non communicable diseases
 Sentinel network keeps a watchful eye on a sample of population by
supplying regular standardized reports on specific diseases and
procedures in Primary health care

Surveillance
 It goes beyond passive reporting of cases
 It includes laboratory confirmation of presumptive diagnosis, finding out
the source of infection, routes of transmission, identification of all cases
and susceptible contacts, and still others who are at risk in order finally to
prevent the further spread of disease
 Serological Surveillance: Identification of pattern of current and past
infection
 Systemic collection of morbidity and mortality data, the orderly
consolidation of these data, special field investigation and rapid
dissemination of this information to those responsible for control or
prevention
 Once the control measures are instituted their effectiveness should be
evaluated. The ultimate goal of Surveillance is prevention.

Health Informatics
• Health informatics is the intersection of information
science, computer science, and health care. It deals
with the resources, devices, and methods required to
optimize the acquisition, storage, retrieval, and use
of information in health and biomedicine. Health
informatics tools include not only computers but also
clinical guidelines, formal medical terminologies, and
information and communication systems. It is
applied to the areas of nursing, clinical care,
dentistry, pharmacy, public health and (bio)medical
research

Scope of health informatics
• Architectures for electronic medical records and other health information systems used for
billing, scheduling, and research
• Decision support systems in healthcare, including clinical decision support systems standards
(e.g. DICOM, HL7) and integration profiles (e.g. Integrating the Healthcare Enterprise) to
facilitate the exchange of information between healthcare information systems - these
specifically define the means to exchange data, not the content
• Controlled medical vocabularies (CMVs) such as the Systematized Nomenclature of Medicine,
Clinical Terms (SNOMED CT), MEDCIN, Logical Observation Identifiers Names and Codes
(LOINC), used to allow a standard, accurate exchange of data content between systems and
providers
• Use of hand-held or portable devices to assist providers with data entry/ or medical decision-
making, sometimes called mHealth.
• The international standards on the subject are covered by ICS 35.240.8in which ISO
27799:2008 is one of the core components.
• Bioinformatics and medical informatics are expected to (partially) converge in the future

Role of Nurse on a health Care
team
• Care of the Patient
• Work with the doctor to cure the patient
• Coordinate the care of the patient
• Protect the patient
• Patient Education
• Advocate for the patient

Epidemiology

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