DR RITESH SHIWAKOTI
MODERN EPIDEMIOLOGY
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)
DEFINATION
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
PURPOSES OF EPIDEMIOLOGY
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
HISTORY
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.
JOHN SNOW
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)
WHO IS AN EPIDEMIOLOGIST ?
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
CLASSICAL VERSUS MODERN
APPLICATIONS
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
MEASURING DISEASE
FREQUENCY
DISEASE FREQUENCY.
DISTRIBUTION OF DISEASE.
DETERMINANTS OF DISEASE.
COMPONENTS OF
EPIDEMIOLOGY
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.
DISEASE FREQUENCY
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.
DISTRIBUTION OF DISEASE
This aspect of epidemiology is known as “analytical
epidemiology”.
Analytical strategies help in developing scientifically sound health
programmes, interventions & policies.
DETERMINANTS OF DISEASE.
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
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
Africa
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)
NAMES OF EPIDEMIOLOGICAL
SOCIETY
Asking questions.
Making comparisons.
EPIDEMIOLOGICAL APPROACH
QUESTIONS RELATED TO HEALTH EVENTS.
QUESTIONS RELATED TO HEALTH ACTION
ASKING QUESTIONS
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?
RELATED TO HEALTH EVENTS.
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?
RELATED TO HEALTH ACTION
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.
MAKING COMPARISION
Measurements of mortality.
Measurements of morbidity.
Measurements of disability.
Measurements of natality.
MEASUREMENTS IN
EPIDEMIOLOGY
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.
The epidemiologist usually expresses disease magnitude as a
RATE, RATIO OR PROPORTION.
TOOLS OF MEASUREMENT
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.
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.
CATEGORIES OF RATE
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.
RATIO
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
PROPORTION
Crude Death Rates.
Specific Death Rates.
Case Fatality Rates.
Proportional Mortality Rates.
Survival Rates.
Adjusted or Standardized Rates.
MORTALITY RATES & RATIOS
Incidence.
Prevalence.
MEASUREMENTS OF MORBIDITY
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
INCIDENCE
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.
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
POINT 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
PERIOD 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
RELATIONSHIP BETWEEN
INCIDENCE & PREVALENCE
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)
CLASSIFICATION OF DISEASE BASED
ON THE FREQUENCY OF
OCCURANCE.
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.
Dengue fever.
Malaria.
leptospirosis,.
Filariasis.
Rabies.
Hepatitis A.
HIV.
Cholera.
Diarrhoea.
LIST OF ENDEMIC DISEASE IN
THE PHILIPPINES
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