This document provides an overview of modern epidemiology. It defines epidemiology as the study of the occurrence and distribution of health-related diseases or events in populations, including their determinants and control. The purposes of epidemiology are described as investigating disease extent and priorities, studying disease progression, identifying causes and risks, recommending interventions, and informing public policy. John Snow is highlighted for his work tracing a cholera outbreak that improved public health systems.

1. MODERN EPIDEMIOLOGY
DR RITESH SHIWAKOTI

2. DEFINATION
Study of the occurrence and distribution of health-related
diseases or events in specified populations, including the study of
the determinants influencing such states, and the application of
this knowledge to control the health problem .
(Porta M, Last J, Greenland S. A Dictionary of Epidemiology, 2008)

3. PURPOSES OF EPIDEMIOLOGY
1. Investigate nature / extent of health-related phenomena in
the community / identify priorities
2. Study natural history and prognosis of health-related
problems
3. Identify causes and risk factors
4. Recommend / assist in application of / evaluate best
interventions (preventive and therapeutic measures)
5. Provide foundation for public policy

4. HISTORY
Epidemiologic transition of the 20th century caused shift in focus
from acute infectious diseases to chronic “life style” diseases
Several exemplar studies are discussed in the chapter
• The British Doctors Study
• The Framingham Heart Study

5. JOHN SNOW
John Snow (15 March 1813 – 16 June 1858) was an English
physician and a leader in the adoption of anaesthesia and medical
hygiene.
He is considered one of the fathers of modern epidemiology, in
part because of his work in tracing the source of a cholera
outbreak in Soho, London, in 1854.
His findings inspired fundamental changes in the water and waste
systems of London, which led to similar changes in other cities,
and a significant improvement in general public health around the
world.

6. WHO IS AN EPIDEMIOLOGIST ?
A professional who strives to study and control the
factors that influence the occurrence of disease or health-related
conditions and events in specified populations and societies, has
an experience in population thinking and epidemiologic methods,
and is knowledgeable about public health and causal inference in
health
(Porta M, Last J, Greenland S. A Dictionary of Epidemiology, 2008)

7. CLASSICAL VERSUS MODERN
Classical:
descriptive,
observational,
field,
analytical,
experimental,
applied,
healthcare,
primary care,
hospital,
environmental,
occupational,
psycho-social, etc
Modern:
risk-factor,
molecular,
genetic,
life-course,
nutritional,
cancer,
disaster, etc
APPLICATIONS

8. MEASURING DISEASE
FREQUENCY
Classifying and
categorizing disease

Deciding what constitutes
a case of disease in a study

Finding a source for
ascertaining the cases
Defining the population at
risk of disease
 Defining the period of
time of risk of disease
Obtaining permission to
study people

Making measurements of
disease frequency
Relating cases to
population and time at risk

9. COMPONENTS OF
EPIDEMIOLOGY
DISEASE FREQUENCY.
DISTRIBUTION OF DISEASE.
DETERMINANTS OF DISEASE.

10. DISEASE FREQUENCY
Refers to the measurement of health related event in the form of
rates & ratios.
E.g.Prevalence rate, Incidence rates, Death rate etc.
These rates are essential for comparing the disease frequency in
different populations or sub groups of the same population.
Such comparison yield valuable information on disease etiology.
This is a vital step in the development of strategies for
prevention of control of health problems.

11. DISTRIBUTION OF DISEASE
The basic tenet of epidemiology is that the distribution of
disease occurs in patterns in a community.
An important function is to study the pattern of the distribution
in various subgroups.
Thus epidemiology examines whether there has been an increase
or decrease over time span.
An important outcome of this step is formulation of etiological
hypothesis.

12. DETERMINANTS OF DISEASE.
This aspect of epidemiology is known as “analytical
epidemiology”.
Analytical strategies help in developing scientifically sound health
programmes, interventions & policies.

13. These aims are achieved by holding scientific meetings and
seminars, by publication of journals, reports, translations of
books, by contact amongst members and by other activities
consistent with these aims. Members are accepted without regard
to race, religion, sex, political affiliation or country of origin

14. The International Epidemiological Association (IEA) was started
in 1954 by John Pemberton of Great Britain and Harold N
Willard of the United States inorder to facilitate communication
amongst those engaged in research and teaching of epidemiology
throughout the world, and to encourage its use in all fields of
health including social, community and preventative medicine.
The IEA is in official relations with the World Health
Organization (WHO) and is run by a Council including Executive
and Regional Councilors for its 7 regions in addition to the Ex-officio
members

15. Africa
NAMES OF EPIDEMIOLOGICAL
SOCIETY
Epidemiological Society of Nigeria
(EPiSON)
Eastern Mediterranean
Saudi Epidemiological Association (SEA)
Lebanese Epidemiological Association
(LEA)
Iranian Epidemiological Association (IrEA)
Europe
Finnish Epidemiological Society (FES).
German Society for Epidemiology (DGEpi)
Spanish Society of Epidemiology (SSE)
Netherlands Epidemiological Society (VvE)
Latin America & Caribbean
The Brazilian Association of Post-
Graduation in Collective Health (ABRASCO)
North America
Society for Epidemiologic Research (SER)
South East Asia
Indian Association of Preventive and Social
Medicine (IAPSM)
Indian Society for Medical Statistics (ISMS)
Indian Public Health Association (IPHA)
Western Pacific
Australasian Epidemiological Association
(AEA)
Japan Epidemiological Association (JEA)

16. EPIDEMIOLOGICAL APPROACH
Asking questions.
Making comparisons.

17. ASKING QUESTIONS
QUESTIONS RELATED TO HEALTH EVENTS.
QUESTIONS RELATED TO HEALTH ACTION

18. RELATED TO HEALTH EVENTS.
What is the event? ( The problem).
What is the magnitude?
Where did it happen ?
When did it happen?
Who are affected?
Why did it happen?

19. RELATED TO HEALTH ACTION
What can be done to reduce this problem and its consequences?
How can it be prevented in future?
What action should be taken by the community? By whom these
activities be carried out?
What resources are required? How are the activities to be
organized?
What difficulties might arise, & how might they be overcome?

20. MAKING COMPARISION
The basic approach in epidemiology is to make comparison &
draw inferences.
This may be comparison of two or more groups.
The first consideration before making .
comparison is to the “comparability”.
Matching or randomization helps in ensuring comparability.

21. MEASUREMENTS IN
EPIDEMIOLOGY
Measurements of mortality.
Measurements of morbidity.
Measurements of disability.
Measurements of natality.

22. Measurement of the presence, absence or distribution of the
characteristic or attributes of the disease.
Measurement of medical needs, health care facilities, utilization
of health services & other related events.
Measurement of the presence, absence or distribution of the
environmental & other factors suspected of the environmental &
other factors suspected of causing the disease.
Measurement of demographic variables.

23. TOOLS OF MEASUREMENT
The epidemiologist usually expresses disease magnitude as a
RATE, RATIO OR PROPORTION.

24. RATE
A rate measures the occurrence of some particular event in a population
during a given time period.
DEATH RATE = Number of deaths in a year *1000
MID YEAR POPULATION
A RATE COMPRISES THE FOLLOWING ELEMENTS.
Numerator,
Denominator,
Time Specification ,
And a Multiplier.

25. CATEGORIES OF RATE
CRUDE RATES : OR UNSTANDARDIZED RATES. Eg :
Birth rates, Death rates.
SPECIFIC RATES : Actual observed rates due to specific causes during
specific time periods .Eg: Tuberculosis – Annual, monthly rates.
STANDARDIZED RATES : These are obtained by direct or indirect
method of standardization .Eg: Age & Sex standardized rate.

26. RATIO
It expresses a relation in size between two random quantities.
The numerator is not a part of the denominator.
Ratio is the result of dividing one quantity by another.
RATIO = x : y or x
y
E.g. : The number of children with scabies at a certain time :
The number of children with malnutrition at a certain time.

27. PROPORTION
A Proportion is a ratio which indicates the relation in magnitude
of a part of the whole.
The numerator is always included in the denominator.
A proportion is usually expressed in percentage.
E.g. The number of children with scabies at a certain time
X 100
The total number of children in the village at the
same time

28. MORTALITY RATES & RATIOS
Crude Death Rates.
Specific Death Rates.
Case Fatality Rates.
Proportional Mortality Rates.
Survival Rates.
Adjusted or Standardized Rates.

29. MEASUREMENTS OF MORBIDITY
Incidence.
Prevalence.

30. INCIDENCE
The number of new cases occurring in a defined population
during a specified period of time.
INCIDENCE =
Number of new cases of specific X 1000
disease during a given period
Population at risk during that time

31. PREVALENCE
Prevalence refers to ALL CURRENT cases (Old & New) existing at a given
point of time, or over a period of time in a given population.
It is actually a ratio.
TYPES OF PREV`ALENCE-
POINT PREVALENCE.
PERIOD PREVALENCE.

32. POINT PREVALENCE
Point Prevalence is defined as the number of all current cases
(old & new) of a disease at one point of time, in relation to a
defined population.
PP =
Number of all current cases (old & new) of a specified
X 1OO
disease existing at a given point in time.
Estimated mid interval population at risk

33. PERIOD PREVALENCE
It measures the frequency of all current cases ( old & new ) existing during a
defined period of time (Annual prevalence).
It includes cases arising before but extending into or through to the year as
well those cases arising during the year.
PP=
Number of existing cases (old & new) of a specified
disease during a given period of time interval x 100
Estimated mid interval population at risk

34. RELATIONSHIP BETWEEN
INCIDENCE & PREVALENCE
Prevalence depends upon : 1. Incidence.
2. Duration of illness.
FORMULA : P = I X D
I = INCIDENCE
D= MEAN DURATION
Therefore, I = P/D
D= P/I

35. CLASSIFICATION OF DISEASE BASED
ON THE FREQUENCY OF
OCCURANCE.
SPORADIC – Occurs occasionally ( Typhoid fever in the U.S.)
ENDEMIC – constantly present in a population (common cold)
EPIDEMIC – many cases in a given area in short period (influenza, Ebola
outbreak in West Africa)
PANDEMIC – a world wide epidemic (influenza occasionally, AIDS might be
considered pandemic)

36. Epidemic
An epidemic occurs when the
incidence rate (i.e. new cases in a given
human population, during a given
period) of a certain disease
substantially exceeds what is
"expected," based on recent
experience.
Disease outbreak that is concentrated
in a particular region.
Pandemic
A pandemic is an epidemic of an
infectious disease that spreads through
human populations across a large
region, like a continent.
Disease outbreak that occurs over a
wide geographic area and affects a very
high proportion of the population.

37. LIST OF ENDEMIC DISEASE IN
THE PHILIPPINES
Dengue fever.
Malaria.
leptospirosis,.
Filariasis.
Rabies.
Hepatitis A.
HIV.
Cholera.
Diarrhoea.