Basic epidemiology

EPIDEMIOLOGY

Bishnuhari Regmi

CDMi, TU, Nepal

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


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.

4/24/2011


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.

4/24/2011


“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)

4/24/2011


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).

4/24/2011


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.

4/24/2011


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.

4/24/2011


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.

4/24/2011


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.

4/24/2011

TERMINOLOGIES IN EPIDEMIOLOGY

The


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


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


.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.

4/24/2011


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.

4/24/2011


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.

4/24/2011


.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.

4/24/2011


.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.

4/24/2011


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.

4/24/2011


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


.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


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.

4/24/2011


Frequency measures used in Epidemiology

4/24/2011


Count, Rate, Ratio, and Proportion

The

4/24/2011


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


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


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.

4/24/2011


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


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

4/24/2011


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.

4/24/2011


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

4/24/2011


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.

4/24/2011


Thank You

Huge

4/24/2011

Basic epidemiology

Health & Medicine

determinants of health

health outcome

determinants determinants

public health practioners

public health departments

disease frequency

bishnuhari regmi cdmi

disease outbreaks