This document provides an overview of epidemiology. It defines epidemiology as the study of disease distribution and determinants in populations. It discusses the history of epidemiology, including John Snow's work identifying contaminated water as the cause of a cholera outbreak. The document also covers epidemiological concepts like the epidemiologic triad of agent, host, and environment; the chain of infection; and the tasks of an epidemiologist like surveillance, investigation, and research.

1. EPIDEMIOLOGY
Submitted by,
A.C. Pournami
IIIrd Year

2. CONTENTS
 INTRODUCTION
 HISTORY
 AIMS OF EPIDEMIOLOGY
 EPIDEMIOLOGIC TRIAD
 CHAIN OF INFECTION
 TASKS OF AN EPIDEMIOLOGIST
 CONCLUSION

3. INTRODUCTION
• Epidemiology is the
cornerstone of public
health, and shapes policy
decisions and evidence –
based practice by
identifying risk factors
for disease and targets
for preventive health
care.

4. DEFINITIONS
• Epidemiology is the branch of medical science
which deals with the treatment of epidemics.
(Thomas Parkin,1873)
• The study of the distribution and determinants
of disease frequency in man. (MacMahon,1960)

5. THE MOST WIDELY ACCEPTED THEORY
• Epidemiology is the study of the distribution and
determinants of health-related states or events, in
specified populations and the application of this
study to the control of diseases and other health
problems.
• (John.M.Last ,1998)

6. ETYMOLOGY
• The word ‘Epidemiology’ is based on the Greek
words :
• Epi = upon, or befall;
• Demos = people
• Logos = study, knowledge

8. HISTORY TIMELINE
CIRCA 400 B.C.
first person known to
have examined the
relationships
between the
occurrence of
disease and
environmental
influences.
Snow conducted
studies of cholera
outbreaks both to
discover the cause of
disease and to
prevent its
recurrence.
Epidemiologists
focused their
methods on acute
infectious and non-
infectious diseases.
There has been an
explosion in the
development of
research methods
and the theoretical
underpinnings of
epidemiology.
1854 1930 - 1940 WORLD WAR

9. HISTORY TIMELINE
Health workers
applied
epidemiologic
methods to
eradicate naturally
occurring smallpox
1970 – 1980 1990
The related fields
of molecular and
genetic
epidemiology
took root

10. 1854
• John Snow, famous for his investigations into the
causes of the 19th century cholera epidemics.
• He is known as the ‘Father of Modern
Epidemiology’.
• Snow conducted studies of cholera outbreaks
both to discover the cause of disease and to
prevent its recurrence.
• This has been perceived as a major event in the
history of public health and regarded as the
founding event of the science of epidemiology
having shaped public health policies around the
world.

11. AIMS OF EPIDEMIOLOGY
• According to the International Epidemiological Association (IEA),
Epidemiology has three main aims :
• To describe and analyse disease occurrences and the distribution in
human populations. (Descriptive Epidemiology)
• To identify the etiologic factors in the pathogenesis of disease.
(Analytical Epidemiology)
• To provide the data essential in planning, implementation and
evaluation of services for the prevention, control and treatment of
disease and setting up priorities among those services.
(Experimental Epidemiology)

12. EPIDEMIOLOGIC TRIANGLE

13. DEFINITION
• The triad consists of external agent, a susceptible host,
and an environment that brings the host and agent
together.
• In this model, disease results from the interaction
between the agent and the susceptible host in an
environment that supports transmission of the agent
from a source to that host.

14. AGENT
• The first link in the chain of disease transmission is
a disease agent.
• The disease may have a single agent, but more
factors are responsible for disease transmission.

15. BIOLOGICAL
PHYSICAL CHEMICAL

16. OTHER AGENTS:
• Mechanical Agents
• Nutritional Agents
• Social Agents
• Hormonal and Chromosomal
factors

17. HOST
• It refers to the human who is susceptible to the disease.
• A variety of factors intrinsic to the host, sometimes called
risk factors can influence an individual’s exposure,
susceptibility or response to a causative agent.
• Susceptibility and response to an agent are influenced by
factors such as age, gender, hereditary, nutrition,
occupation, custom habits, immunity, marital status,
socio-economic status and life-style factors.

18. ENVIRONMENT
• It refers to extrinsic factors that affect the agent and the
opportunity for exposure.
• Environmental factors such as geology, and climate,
biologic factors such as insects that transmit the agent,
and socio-economic factors such as crowding, sanitation,
and the availability of health services.

19. TYPHOID FEVER
Polluted water.
Open
defecation.
Salmonella
Typhi
Young age,
more in the
males, low
immunity
power, lack of
personal
hygiene

20. CHAIN OF INFECTION
• The traditional epidemiologic triad model holds that infectious
diseases results from the interaction of agent, host and environment.
• Transmission occurs when the agent leaves its reservoir or host
through a portal of exit, is conveyed by some mode of transmission
and enters through an appropriate portal of entry to infect a
susceptible host. This sequence is sometimes called the chain of
infection.

22. PORTAL OF EXIT : The path by which an
pathogen leaves the host.
MODE OF TRANSMISSION : An infectious agent
may be transmitted from its natural reservoir to a
susceptible host in different ways.
PORTAL OF ENTRY : The portal of entry refers to
the manner in which a pathogen enters a
susceptible host.
SUSCEPTIBLE HOST : It depends on the genetic,
constitutional factors, specific immunity, and non-specific
factors that affect an individual’s ability to resist infection or
to limit the pathogenicity.
RESERVOIR : The habitat in which the agent
normally lives, grows and multiplies.

23. DISEASE PREVENTION
AND CONTROL
• Knowledge of the portals of exit and entry and
modes of transmission provides a basis for
determining appropriate control measures.
• Early diagnosis
• Epidemiological Investigation
• Isolation
• Treatment
• Quarantine

24. TASKS OF AN EPIDEMIOLOGIST
• Surveillance
• Investigation
• Analysis and Interpretation
• Communication
• Evaluation
• Research
• Management

25. CONCLUSION
• As the basic science of public health, epidemiology includes the study of
frequency, patterns, and causes of health-related states or events in populations,
and the application of that study to address public health issues.
• Epidemiologists use a systematic approach to assess the What, Who, Where,
When, and Why/How of these health states or events.
• Core epidemiologic tasks of a public health epidemiologist include public health
surveillance, field investigation, research, evaluation, and policy development. In
carrying out these tasks, the epidemiologist is almost always part of the team
dedicated to protecting and promoting the public's health.

26. REFERENCES
• SOBEN PETER - ESSENTIALS OF PUBLIC HEALTH DENTISTRY
(5th Edition)
• https://en.wikipedia.org/wiki/Epidemiology
• http://www.who.int/topics/epidemiology/en/