Introduction to epidemiology

As per John M. Last (1988) Epidemiology is 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.

1. Epidemiology

2. Epidemiology
EpidemiologyisthebasicscienceofcommunityMedicine.
‘Epi’–among‘demos’–people‘logos’–study
Epidemiologymeansthestudyamongpeople.

3. Definition of Epidemiology
•As per Perkins (1873) It is that branch of science
which treats of epidemics.
•As per Frost (1927) it is the science of mass
phenomenon of infectious disease.
•As per Greenwood (1934) The study of any
disease as a mass phenomena.
•As per MacMohan (960) The study of the
distribution and determinants of disease frequency
in man.

4. Definition of Epidemiology
AsperJohnM.Last(1988)Epidemiologyisthe
studyofthedistributionanddeterminantsof
healthrelatedstatesoreventsinspecified
populations,andtheapplicationofthisstudyto
thecontrolofhealthproblems.

5. Epidemiology often more concerned with the well-
being of society as a whole, than with the well-
being of individuals.
In these definition three components are common.
•Study of the disease frequency (frequency of
disease, disability or death and summarizing in the
form of rates and ratios).
•Study of the distribution (pattern of disease i.e.
time, place, person).
•Study of the determinants (underlying cause or risk
factors).

6. Components of Epidemiology
1) Disease frequency (rate or ratio)
2) Distribution of disease (Time, place &
person)
3) Determinants of disease (Cause or risk
factor)

7. •DISTRIBUTION
•TIME :-WHEN OCCURRED
•PLACE :-WHERE IT OCCURRED
•PERSON :-AGE, SEX, RACE, OCCUPATION

8. DETERMINANTS
(CAUSES & FACTORS THAT INFLUNCE THE RISK OF DISEASE )
•HOST FACTORS:-
Factors that determine the host exposure :-age, sex,
genetic, physiology, nutritional status, constitutional
make up, previous immunological experience,
occupation.

9. Aims of Epidemiology
According to IEA (International Epidemiological Association),
1.To describe the distribution and magnitude of health and disease
problems in human population.
2.To identify the aetiological factors and risk factors in pathogenesis of
disease.
3.To provide data essential to planning implementation and evaluation
of services for prevention, control and treatment of diseases and
setting of priorities among the services.

10. The ultimate aim of epidemiology is to lead effective action
1.To eliminate or reduce health problems or its consequences.
2.To promote the health and well being of society as a whole.

11. Difference of Epidemiology & Clinical Medicine
CLINICAL MEDICINE EPIDEMIOLOGY
1.The unit of study is case or cases 1.Unit of study is the population
2.Concerned with disease in
person
2.Concerned with disease pattern
in population both sick &
healthy
3.Clinician gives diagnosis and
treatment & prognosis of the
case. The diagnostic techniques
are refined and modified
3.Epidemiologist is interested in
the source of infection, mode of
spread & trend of disease.
Evaluates the outcome of
preventive & therapeutic
measure & give clue to
administrator for effective
management
4.The patient goes to the clinician.4.Epidemiologist goes to the
community.

12. Epidemiological Approach
The epidemiological approach to the problems of health and
disease is based on two major foundations
•Asking Questions
•Making comparisons

13. Asking Questions
Epidemiology has been defined as “a means of
learning or asking questions… and getting
answers that lead to further questions.”
Related to health Events
a.What is the problem?
b.What is its Magnitude?
c.Where did it happen?
d.When did it happen?
e.Who are affected?
f.Why did it happen?

14. Cont……
•Questions Related to Health Action
a.What can be done to reduce the
problem?
b.How can it be prevented?
c.What action should be taken by the
community? By the Health Services? By
other sectors?
d.What resources are required?
e.How are the activities to be organized?
f.What difficulties may arise in
implementation?

15. Making Comparisons
•The basic approach in epidemiology is to make comparisons and draw
inferences.
•Comparison between two or more groups
(one group having disease or exposed to risk factors and the other group
not having disease or not exposed to risk factors, or comparison
between two individuals).
•Epidemiologist weighs, balances and contrasts.

16. Uses of Epidemiology
1.In health care management
•Making Community diagnosis
•Planning and evaluation of health services.
•Developing health policies.
2.Understanding disease process
•Studying natural history of disease.
•Searching for causes and risk factors.
•Historic studies of rise & fall of disease.
•Identification of syndromes.

17. Uses of Epidemiology
3. Uses in public health practice
•Investigation of epidemics
•Surveillance of disease
•Making projection for future
•Formulating medical teaching curricular
4. Assisting in Clinical Practice
•Assessing effectiveness of treatment modalities
•Assessing effectiveness of preventive modalities
•Studying prognostic factor
•Studying effectiveness of diagnostic modalities
•Assisting in clinical decision making
•Indispensable for basic planning, conducting and analysing clinical research

18. DISEASE FREQUENCY
RATE :
Signifies speed or the frequency of occurrence per unit of
time.
•The numerator is a part of the denominator.
Eg.Notification rate of new sputum smear +ve cases = New
ss +ve / 100,000 population.(38 in 2002)
•Cure rate :No. of cases curedx100
No. Of cases under Trt.

19. RATIO :A number or quantity of one item in comparision to
the other.
Both the items are not a part of each other.
Eg. Sex ratio
1.New smear +ve : New smear -ve
2.New smear +ve : Extra pulmonary
3.Non seriously ill extra pulm. :Seriously ill extra pulm.
PROPORTION :Measurement of the size of a part out of
the whole, usually the whole taken as 100.
If the fraction is too small, the base can be 1000 or any
10
x
.
Numerator is always a part of a denominator.

20. Terminology used in Epidemiology
Epidemic –The unusual occurenceof disease, specific health
related behaviour (eg. Smoking) or other health related
events (eg. Traffic accidents) in a community or region clearly
in excess of “expected occurence.”
Endemic –constant presence of a disease or infectious agent
within a given geographic area or population group, without
importation from outside throughout the year in certain parts
of country.
Sporadic –Scattered outbreaks of infectious disease in
different parts.
Pandemic –An epidemic usually affecting a large proportion of
population occurring over a wide geographic area.

21. Exotic –Infection is imported from outside.
Zoonoses –Infectious disease of animals transmitted to man.
Eg. Rabies, plague
Carrier –A person or animal who harbouring specific
infectious agent without showing signs and symptoms of
the disease.
Communicable disease –Illness transferred directly or
indirectly from the sick to the healthy person.
Surveillance –The continuous scrutiny of the factors that
determine the occurrence and distribution of disease and
other conditions of ill health.
Eradication –Termination of all transmission of infection by
extermination of infectitious agent through surveillance and
containment.