Introduction to Epidemiology

Manish Chaudhary

Basic Concept in EpidemiologyEpidemiology is the study of the occurrence, distribution and determinants of health problems and diseases in human population or communities and the use of this knowledge for prevention and control of diseases.The primary unit of concern is a group of person not any single person. Therefore epidemiology deals with population pathology not the clinical pathology.

Word “Epidemiology” is derived from Greek words: Epi= upon , onDemos= peopleLogus= study, knowledge

Definitions of Epidemiology

• It is branch of medical science that treats epidemics –Parkin

• Science of mass phenomenon of infectious diseases- Frost

• Study of disease, any disease, as a mass phenomena- Greenwood

• A shorter definition is the “study of the occurrence of illness" -Gayord Anderson

• “The study of the frequency, distribution and determinants of disease in human population" - Mac Mohan and Pugh

A longer definition is “the study of distribution and determinants of health related states and events in specified populations, and the application of this study to control of health problems"-Last, 1988

These definitions are essentially same and rest upon two fundamental assumptions: Human disease does not occur at randomHuman disease has causal and preventive factors that can be identified through systematic investigation of different populations or subgroups in different places or different times.

Three important components included in these definitions are:

• Frequency• Distribution• Determinants

• The first component to be considered is measurement of disease frequency, which involves quantification of the occurrence of disease.

• The second component is distribution of disease in terms of time, place, and person- who is getting the disease, where and when the disease is occurring.

• The third component, the determinant of disease derives from the first two, since knowledge of frequency and distribution of disease is necessary to test an epidemiological hypothesis.

Functions/Uses of epidemiology

1. To find causation of the disease2. To describe natural history3. Description of health status of populations 4. Evaluation of intervention 5. Community diagnosis6. Planning and evaluation7. Syndrome identification

Aims of epidemiology

• To describe the distribution and size of disease problems in human populations. (Descriptive epidemiology)

• To identify the etiological factors in the pathogenesis of disease (Analytical epidemiology)

• To provide the data essential in planning, implementation and evaluation of services for the prevention, control and treatment of disease and setting up priorities among those services.(Experimental epidemiology)

The ultimate aim of epidemiology is – to eliminate or reduce the health problem or its

consequences– to improve medical care and provide

administrative guidance for community health services

– to promote the health and well being of society as a whole

Scope of epidemiology• Disease definition: characteristics or combination of character

that best discriminate disease from non diseased• Disease occurrence: the rate of development of new case in

population. The proportion of current disease within population• Disease causation: the risk factors for disease development and

their relative strength with respect to an individual and population

• Disease outcome: the outcome following disease onset and of the risk factors.

• Disease management: the relative effectiveness of proposed therapeutic interventions

• Disease prevention: the relative effectiveness of proposed preventive strategies including screening

Comparison between Epidemiology and Clinical MedicineSubjects Epidemiology Clinical Medicine

Unit of study Defined population or population at risk Case or cases

Examination Survey of particular community patients

Concern with Both sick and healthy people Cases with disease pattern

Diagnosis People/ community diagnosis Patients diagnosis with the help of signs and symptoms

Objective To identify particular source of infection, mode of transmission, aetiological factors, ways of controlling these problems and continuous follow up

To diagnose, prognosis and prescribe specific treatment for the diseases within limited period of time

Relationship Epidemiological team goes to community to find and solve health problem

Patient come to the doctor for treatment

Area concern Concern with preventive and promotive measure

Concern with curative measure

Concept Biostatistical Biomedical

Result Symbolized in the form of tables and graphs Symbolized as medical and laboratory report

Time Sustainable and long process Quick and short result

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