Introduction to Epidemiology Manish Chaudhary

Basic Concept in Epidemiology Epidemiology 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, on Demos= people Logus= 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 random Human 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 disease 2.To describe natural history 3.Description of health status of populations 4.Evaluation of intervention 5.Community diagnosis 6.Planning and evaluation 7.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 Medicine SubjectsEpidemiologyClinical Medicine Unit of studyDefined population or population at riskCase or cases ExaminationSurvey of particular communitypatients Concern withBoth sick and healthy peopleCases with disease pattern DiagnosisPeople/ 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 ConceptBiostatisticalBiomedical ResultSymbolized in the form of tables and graphs Symbolized as medical and laboratory report TimeSustainable and long processQuick and short result

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