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