Derived from word “Epidemic”
Epi ------------------ means --------- Among
Demos -------------- means --------- People
Logos --------------- means --------- Study
“Study of distribution frequency & determinants of health related states in specified population”
“It is the study of the causes and distribution of disease in human populations.”
According to WHO
“Epidemiology is the study of the distribution and determinants of health-related states or events
(including disease), and the application of this study to the control of diseases and other health
Determinants: Causes and other factors that influence the occurrence of disease and other health-related events
Components of epidemiology:
Disease frequency
Distribution of disease
Determinants of disease
Difference b/w Epidemic & Pandemic:
“Unusual occurrence of disease in a population in
excess of its expected frequency and if disease is
not prevalent then presence of at least two cases of
that disease at same place”
“If a disease spreads over a very large
geographical area and affects a major portion of
population of world, it is called pandemic”
Chicken pox, Cholera
Influenza pandemic in 1918 & 1957
Cholera pandemic in 1962
Pandemic refers to an epidemic that has spread over
Epidemic refers to an increase, often sudden, in the several countries or continents, usually affecting a
number of cases of a disease above what is normally large number of people.
expected in that population in that area.
Outbreak: It carries the same definition of epidemic, but is often used for a more limited geographic area
Endemic: It refers to constant presence and/or usual prevalence of a disease or infectious agent in a
population within a geographic area
An epidemiological approach helps planners
a. To focus on the main problems of a community rather than of individual patients &
b. To identify measures for improving the health of the community as a whole
Epidemiology can increase the general understanding about a disease and particularly
how it is transmitted even when the cause is unknown. In epidemiology, the assumption
is that diseases do not occur randomly, but follow predictable patterns that can be studied
and expressed in terms of
What, Who, Where, When, How, Why, and What next
The goal of epidemiology is to identify subgroups of the population who are at a higher
risk of disease than usual and who will benefit the most from disease specific
interventions. Epidemiological information can be used to develop prevention strategies
according to:
a. Time (peaks at a particular season)
b. Place (limited to specific geographic areas)
c. Person (groups at risk)
Epidemiology in emergencies:
Epidemiology in emergencies goes beyond simply understanding how diseases are
contracted and spread.
Objectives of epidemiology in emergencies
 Identifying the priority health problems in the affected community
 Determining the extent of disease existing within a community
 Identifying the causes of disease and the risk factors
 Determining the priority health interventions
 Determining the extent of damage and the capacity of the local infrastructure
 Monitoring health trends of the community
 Evaluating the impact of health programs
Epidemiological indicators:
Indicators are measures that reflect
 State of a population in terms of health, socioeconomic status etc
 Process and outcome of existing services
Indicators are useful for measuring and describing the effects of a disaster on a population and
for providing baseline measurements. Later, these measurements will help determine the
outcome of the relief response.
Types of Indicators: Indicators may be defined from surveys or an existing health information
system. They might be
i. Quantitative or
ii. Qualitative
Qualitative indicators:
Quantitative indicators:
These are easily calculated from numeric information such These indicators measure people’s attitudes and
as the total number of people, the number of people knowledge and are more difficult to measure. These
according to age and sex etc
indicators might be critical in explaining unexpected
values of quantitative indicators.
Examples of quantitative indicators include:
Examples of qualitative indicators include:
Incidence: No. of cases or events that occur within a Awareness of the value of immunization: Low awareness
defined e.g. incidence of measles among children
may explain the high incidence of measles in a
population living within five kilometres from a health
Prevalence: Proportion of population with particular facility
condition that is divided by total number of persons at risk Adherence to preventive interventions against
for condition during that period
HIV/AIDS: Poor compliance from youths in preventive
e.g. prevalence of HIV/AIDS in a population.
interventions (e.g.; A lack of understanding about“Be
Faithful, Use a Condom” program) might explain the
Morbidity rate: All persons in the population under increasing prevalence of HIV/AIDS in a population
consideration e.g. belonging to a specific gender or age- Equity in distribution of resources: Inequitable
group who become clinically ill during the specific period distribution of food might explain the increased mortality
detected in a subgroup of a population
Mortality rate: Number of deaths occurring in a Barriers to seeking treatment for malaria: Barriers to
population in a specific period (usually a year) divided by seeking treatment such as unaffordable health services,
the number of persons at risk of dying during that period
might explain an increase in malaria-specific mortality
e.g., mortality rate of infants during their first year of life
It describes operation aimed at reducing
Incidence of disease
Duration of disease and consequently risk of transmission
Effects of infection, including both physical and psychological complications
Financial burden community
“Action taken prior to the onset of disease, which
removes possibility that a disease will ever occur”
“Any attempt to intervene or interrupt usual sequence in
the development of disease in man”
Level of prevention:
Methods of intervention:
Primordial: Prevention in chronic diseases by
Health promotion: Process to improve health
changing in lifestyle e.g. DM, CHF
through education, environmental modification,
Primary: Applied in pre pathogenesis phase:
medical checkups and healthy life style
Secondary: Applied in pathogenesis phase: Halts
Specific protection: measures applicable to
progress of disease: Tool for control of
intercept cause of disease before involvement e.g.
immunization against diseases
Tertiary: Applied in late pathogenesis phase: All
Early diagnosis & prompt treatment
measures to reduce impairments & sufferings
Disability limitation: Lack of ability to perform
activity within range
Rehabilitation: Combined coordinated use of
medical, social, educational and vocational
measures for training individuals to functional
 Epidemiology and surveillance, Public health guide for emergencies, The Johns Hopkins
and the International Federation of Red Cross and Red Crescent Societies, 220-283
 http://www.who.int/topics/epidemiology/en/