1. Introduction to Epidemiology
Manish Chaudhary

2. 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.

3. Word “Epidemiology” is derived from Greek words:
Epi= upon , on
Demos= people
Logus= study, knowledge
Thus epidemiology in its broadest sense is the study of effects of various things on people.

4. The evolutions of Definitions of Epidemiology
Historical definition “The science and doctorine of epidemics”( New standard dictionary of English Language)
The science of epidemics and epidemic disease.( stedmans practical medical dictionary)
The science of mass phenomena of infectious disease or the natural history of infectious diseases ( Frost, 1927)
The science of infective diseases, their prime causes, propagation and prevention(Stallybrass, 1931)
Study of disease, any disease, as a mass phenomena-(Greenwood 1932)

5. Modern Meaning
Epidemiology is the science which concerns itself with the natural history of disease as it is expressed in groups of persons related by some common factors of age, sex, race, location or occupation as distinct from the development of disease in an individual.( American Epidemiological Society)
Epidemiology is the study of the pattern of diseases and the factors that cause disease in man( CDC, US Public health services)
“The study of the frequency, distribution and determinants of disease in human population" - Mac Mohan and Pugh

6. A widely accepted 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

7. Three important components included in these definitions are:
Frequency
Distribution
Determinants

8. 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.

9. 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)

10. 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

11. Functions/Uses of epidemiology
To find causation of the disease
To describe natural history
Description of health status of populations
Evaluation of intervention
Community diagnosis
Planning and evaluation
Investigate epidemics of unknown etiology
Elucidate mechanism of disease transmission

12. 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

13. Comparison between Epidemiology and Clinical Medicine
Subjects
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

14. Thank You