Basic epidemiology
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Transcript of Basic epidemiology
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EPIDEMIOLOGY
Bishnuhari Regmi
CDMi, TU, Nepal
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By Bishnuhari Regmi 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?4/24/2011
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By Bishnuhari Regmi 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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By Bishnuhari Regmi 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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By Bishnuhari Regmi 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).”
DeterminantsDistributionPopulationHealth phenomena (morbidity, mortality)
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By Bishnuhari Regmi 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 carcinogensOther 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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By Bishnuhari Regmi 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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By Bishnuhari Regmi 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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By Bishnuhari Regmi 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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By Bishnuhari Regmi 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.
To control the distribution of disease, the epidemiologic approach is used to prevent the occurrence of new cases of disease, to eradicate existing cases, and to prolong the lives of those with the disease.
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TERMINOLOGIES IN EPIDEMIOLOGY
The
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By Bishnuhari Regmi 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 invasion of the gut by helminthes4/24/2011
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By Bishnuhari Regmi 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
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By Bishnuhari Regmi 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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By Bishnuhari Regmi 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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By Bishnuhari Regmi 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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By Bishnuhari Regmi 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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By Bishnuhari Regmi 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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By Bishnuhari Regmi 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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By Bishnuhari Regmi 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
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By Bishnuhari Regmi 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
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By Bishnuhari Regmi 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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By Bishnuhari Regmi 23
Frequency measures used in Epidemiology
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By Bishnuhari Regmi 24
Count, Rate, Ratio, and Proportion
The
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By Bishnuhari Regmi 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 Chitawan4/24/2011
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By Bishnuhari Regmi 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. 4/24/2011
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By Bishnuhari Regmi 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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By Bishnuhari Regmi 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)4/24/2011
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By Bishnuhari Regmi 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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By Bishnuhari Regmi 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 a disease over a specified period of time, and the denominator is a unit size of population.
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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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By Bishnuhari Regmi 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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By Bishnuhari Regmi 33
Thank You
Huge
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