Concept and Basic principles of Epidemiology

1. EPIDEMIOLOGY
Public Health and
Environment
By Iman Haroon
Department of
Environmental Sciences
GCWUS

2. CONCEPT
Epidemiology is the study and analysis of the distribution, patterns
and determinants of health and disease conditions in defined
populations.

3. EPIDEMIOLOGY AND PUBLIC
HEALTH: LINKAGE
•It is a cornerstone of public health, and
shapes policy decisions and evidence-based
practice by identifying risk factors for
disease and targets for preventive healthcare.
• Epidemiology provides us with information
and methods that help control the spread of
disease.

4. Incidence
Incidence refers to the occurrence of
new cases of disease or injury in a
population over a specified period of
time.
Example: a person developing diabetes,
becoming infected with HIV, starting to
smoke, or being admitted to the hospital
Prevalance
Prevalence is the proportion of a particular
population found to be affected by a medical
condition at a specific time.
Number of previous and new cases.
Example: the prevalence of obesity among
American adults in 2001 was estimated by the
U. S. Centers for Disease Control (CDC) at
approximately 20.9%.

5. Mortality Rtae
Mortality rate, or death
rate, is a measure of the
number of deaths in a
particular population,
scaled to the size of that
population, per unit of
time.
Formula: Number of
deaths per 1000 people
Morbidity Rate
The rate at which a
disease occurs in a
population.
Formula: Dividing the
number of affected
individuals by the total
number of individuals
within a specific
population
Frequency
Frequency is the
number of occurrences
of a repeating event per
unit of time.

6. DISEASE IN POPULATION
Epidemic
An epidemic is the rapid spread of
disease to a large number of
people in a given population
within a short period of time.
Example: Yellow fever, smallpox,
measles, and polio are prime
examples of epidemics that
occurred throughout American
history
Endemic
An infection is said to be endemic in a
population when that infection is
constantly maintained at a baseline
level in a geographic area without
external inputs.
Example: chickenpox is endemic in
the United Kingdom, but malaria is
not. Polio is endemic in Pakistan.
Pandemic Sporadic
A pandemic is an epidemic of an
infectious disease that has spread
across a large region, for instance
multiple continents or worldwide,
affecting a substantial number of
individuals.
Example: The 1918 Spanish flu
Sporadic is a term used to refer to a
disease which occurs only infrequently,
haphazardly, irregularly or occasionally
from time to time in a few isolated
places with no discernible temporal or
spatial pattern, as opposed to a
recognizable epidemic or endemic
pattern.

7. EPIDEMIOLOGICAL
STUDIES
Descriptive
Descriptive epidemiology
uses observational studies of the
distribution of disease in terms of
person, place, and time.
Only one group studied
Used for: program planning,
generating hypotheses, suggesting
ideas.
Analytical
The search for causes and
effects, or the why and the how.
To test the hypotheses
Requires more resources and
specialized knowledge
At least two groups are studied
for comparison

8. EXPERIMENTAL EPIDEMIOLOGY
Experimental epidemiology is the study of the relationships of
various factors determining the frequency and distribution of
diseases in a community.
Experimental epidemiology contains three case types:
randomized control trial (often used for new medicine or drug
testing), field trial (conducted on those at a high risk of
conducting a disease), and community trial (research on social
originating diseases).
The method employs prospective population experiments
designed to test epidemiological hypotheses, and usually
attempt to relate the postulated cause to the observed effect.
Trials of new anthelmintics are an example.

9. Reservoirs of Infections: The reservoir of an infectious
agent is the habitat in which the agent normally lives,
grows, and multiplies.

10. PORTALS OF ENTRY
AND EXIT