This is all about basic epidemiology.

1. Bishnuhari Regmi
CDMi, TU, Nepal

2. General questions answered by
epidemiology
 When there is a linkage between a factor (i.e., as
contaminants in food and water) and a health
outcome (e.g. diarrhea), does this observation
mean that the factor is a cause of disease?
 If there is an association? Does the amount of
disease vary according to the amount of exposure
to the factor?
 Based on the observation of such an association,
what practical steps should individuals and public
health departments take? What should the
individual consumer do?
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3.  Do the findings from an epidemiologic study merit
panic or a measured response?
 How applicable are the findings to settings other that
the one in which the research was conducted? What
are the policy implications of the findings?
 Epidemiology is a discipline that describes, quantifies,
and postulates causal mechanisms for health
phenomena in populations.
 Using the results of epidemiologic studies, public
health practioners are aided in their quest to control
health problems such as disease outbreaks.
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4. Definition of Epidemiology
 The word epidemiology derives from epidemic, a term
that provides an immediate clue to this subject matter.
Epidemiology originates from the Greek words:
epi = upon
demos = people
logos = study of
“The study of the distribution and determinants of
health-related states or events in specified
populations, and the application of this study to
the control of health problems” – John M. Last,
1988.
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5. “Epidemiology is concerned with the distribution
and determinants of health and diseases,
morbidity, injuries, disability, and mortality in
populations. Epidemiologic studies are applied
to the control of health problems in
populations. The key aspects of this definition
are determinants, distribution, population and
health phenomena (e.g., morbidity and
mortality).”
Determinants
Distribution
Population
Health phenomena (morbidity, mortality)
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6. Determinants
 Determinants are factors or events that are
capable of bringing about a change in
health.
 Some examples are –
Specific biologic agents (e.g., bacteria) that are
associated with infectious diseases, or
Chemical agents that may act as carcinogens
Other potential determinants for changes in
health may include less specific factors, such as
stress or adverse lifestyle patterns (lack of
exercise, or a diet high in saturated fats).
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7. Distribution
 Frequency of disease occurrence may vary
from one population group to another.
 For example, hypertension may be common
among young African-American men than
young White men; malaria is more common in
terai region of Nepal than hilly and mountain
region
 Such variations in disease frequency illustrate
how disease may have different distribution
depending upon the underlying characteristics
of the populations being studied.
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8. Population
 Examines disease occurrence among population
groups rather than among individuals.
 Epidemiology is often referred as “population
medicine”.
 The epidemiologic and clinical descriptions of a
disease are quite different as a result. For example –
 Clinical description of disease would include signs and
symptoms, such as fever, headache, vomiting, nausea, etc.
 Epidemiological description would indicate which age
groups would be most likely to be affected time trends,
geographic trends, and other variables that affect the
distribution of disease.
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9. Health outcomes
 Epidemiology is used to investigate many different
kinds of health outcomes.
 These range from infectious diseases to chronic
disease, and various states of health, such as
disability, injury, limitations of activity, and mortality.
 Other health outcomes have included positive
functioning of the individual and active life
expectancy as well as health related events,
including mental disorders, suicide, substance
abuse, and injury.
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10. Aims/Scope of Epidemiology
 As the basic method of public health, epidemiology is
concerned with efforts to describe, explain, predict, and
control. i.e.
 To describe the health status of populations means to
enumerate the cases of disease, to obtain relative
frequencies of the disease within subgroups, and to
discover important trends in the occurrence of disease.
 To explain the etiology of disease means to discover
causal factors as well as to determine modes of
transmission.
 To predict the occurrence of disease. Such information is
crucial to planning interventions and allocation of
healthcare resources.
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11. The

12. Terminologies in
EpidemiologyInfection
 The entry and development/multiplication of an
infectious agent in the body of man and animals.
 There is successful entry and growth of disease
agents with the production of changes in the host,
which may be hypersensitivity/allergy, disease,
immunity
Infestation
 The lodgement, development or reproduction of
arthropods on the surface of the body. Or the
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13. Case
 A person in the particular place or in a study,
suffering from a particular disease or disorder or
condition under studied/ investigation.
Primary case
 The individual who introduces the disease into the
family or group under study or the first case of
communicable disease, that introduces into a
community under study.
Secondary case
 An individual, who develops a disease after being
exposed with the primary case.4/24/2011 By Bishnuhari Regmi 13

14. .Index case..
 The first case of communicable disease in a family
or other defined group under study, that comes to
the attention of the investigator.
Carrier
 An infected person or an animal that harbors a
specific disease agent with or without suffering from
the disease, there may or may not be recognizable
clinical manifestation of the disease but they are
capable to transmit infection to others.
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15. Agent
 An agent is a substances, which may be living, non-
living or a force which is tangible or intangible whose
presence, relative excess or relative lack is enough for
disease.
Host
 A person or other animal including birds and arthropods,
that subsistence or provides logments to an infectious
agent under natural conditions.
Environment
 The aggregates of all those external and internal
factors/forces, tangible or intangible, living or non-living
which is directly or indirectly related to the health and
survival of human beings or other living creatures.
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16. Sporadic
 The cases or disease which occurs irregularly,
haphazardly from time to time and generally
infrequently.
Endemic
 It is usual frequency of a disease occurrence.
The conditions in which there is habitual
presence of a disease or its agents within a given
geographical area or population group.
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17. .Epidemic
 The unusual occurrence of disease in a community
or a specific region in the light of past experiences,
it is the proportions of disease frequency beyond
expectation.
Pandemic
 An epidemic usually affecting a large proportion of
the population, it is the occurrence or spread of an
epidemic over a wide geographical area. Such as a
section of a nation, entire nation or worldwide.
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18. .
Source
 The person, animal or object or substances from
which an infectious agent pass or is disseminated
to the host.
Common source
 It refers single exposure, or point source or
continuous or multiple exposure of epidemics.
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19. Surveillance
 It can be viewed from different ways –according to
one view; surveillance means to watch over with
great attention, authority and often with suspicion.
 It is an ongoing systematic collection, collation,
analysis and interpretation of data and
dissemination of information to who need to know
in order that action may be taken.
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20. .
Opportunistic infection
 It is the infection by agent/organism that takes the
opportunity provided by an alteration in host
defense mechanism and hence cause disease.
Eradication
 It is the process or state in which there is
termination of all transmission of infection by
extermination of infectious agent through the
surveillance system and containment.
Contagious Disease
 The disease/infection that is transmitted through
the contact like scabies, leprosy, trachoma.4/24/2011 By Bishnuhari Regmi 20

21. .Communicable Disease
 An illness due to specific infectious agent or its toxic
products capable of being directly or indirectly
transmitted to man to man or animal to animal or from
the environment to man or animal.
Epizootic
 An outbreak of disease in animal population - anthrax,
rabies, brucellosis
Epornithic
 An outbreak of disease in birds population
Air borne infection
 It is a mode of transmission of infection, which takes
place through air.4/24/2011 By Bishnuhari Regmi 21

22. .
Incubation period
 The time interval between invasion of microorganism
and the development of first sign/symptoms of a
disease cause by the same microorganism. Incubation
is some time also called generation time.
Generation time
 The time interval between receipt of infection by a host
and maximal infectivity of that host.
Latent infection
 The condition in which the host does not shed the
infectious agent that lies dormant within the host
without symptoms.
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23. Frequency measures used in
Epidemiology
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24. Count, Rate, Ratio, and
Proportion
 The
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25. Count
 The simplest and most frequently performed
quantitative measure in epidemiology.
 a count simply refers to the number of cases of a
disease or other health phenomenon being studied.
 Examples of counts include the number of:
 Cases of avian influenza reported in Kathmandu valley
during January of a particular year
 Road accident deaths in Kathmandu valley during a 24-
hour period
 Blood donors in a blood donation program organized by
Nepal Red Cross Society in Chitawan
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26. Ratio
 A ratio is defined as “the value obtained by dividing
one quantity by another”.
 A ratio consists of a numerator and a denominator.
 The numerator is not a component of the denominator.
 The most general form of a ratio does not necessarily
have any specified relationship between the numerator
and denominator, but, however expresses a relation in
size between two random quantities.
 The numerator and denominator may involve an
interval of time or may be instantaneous in time.
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27.  A ratio may be expressed as follows: ratio = X/Y,
or X:Y. i.e.
Ratio = Numerator (X)
Denominator (Y)
 For example, of 1,000 motorcycle fatalities, 950
victims are men and 50 are women. Then sex ratio
for motorcycle fatalities is:
Number of male cases
Number of female cases
i.e. 950/50 = 19:1 male to female.
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28. Proportion
 A proportion is a type of ratio in which the numerator is
part of the denominator.
 It is a ratio which indicated the relation in magnitude of
a part of the whole.
 A proportion is usually expressed as percentage. And
is also usually measured at a point of time.
 It is normally expressed as follows: proportion =
X/(X+Y). i.e.
Proportion = Numerator (X)
Denominator (X+Y)
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29.  For example,
The number of children with scabies at a certain
time ×100%
The total number of children in the village at the
same time
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30. Rate
 A rate measures the occurrence of some particular
event (development of disease or the occurrence of
death) in a population during a given time period.
 It is also a type of ratio, and differs from a proportion
because the denominator involves a measure of
time.
 It is very important to remember that, to calculate a
rate, two periods of time are involved; the beginning
and end of the period.
 The numerator consists of the frequency of a4/24/2011 By Bishnuhari Regmi 30

31.  In other words, a rate comprises the following
elements – numerator, denominator, time
specification, and multiplier
 An example of a typical death rate is the death
rate. It is written as below:
Death rate =
Number of deaths in a given year ×
1,000 or 100,000
Reference population i.e. Mid-year population of that
year
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32. The various categories of rates are:
 Crude rates: These are the actual observed rates
such as the birth and death rates. Crude rates are
also known as unstandardized rates.
 Specific rates: These are the actual observed
rates due to specific causes (e.g., tuberculosis); or
occurring in specific groups (e.g., age-sex groups)
or during specific time periods (e.g., annual,
monthly or weekly rates).
 Standarized rates: These are obtained by direct
or indirect metnod of standardization or
adjustment, e.g., age and sex standardized rates.
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33. Thank You
 Huge
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