1. Prof. Saman Wimalasundera
MBBS DO PhD
Professor in Community Medicine
Former Head, Department of Community Medicine
In charge Ophthalmologist
Community Ophthalmology center
Faculty of Medicine
University of Ruhuna
Galle
Sri Lanka

2. Epidemiology and its application

3. The concepts of epidemiology were first
suggested by Hippocrates in the fifth century
B.C. that the development of human disease
might be related to external and personnel
environment of an individual.

4. The word epidemiology is derived from
Greek and means “Studies upon people”
Epi – Upon, Demos – People, Logia – Study
In contrast to clinical medicine epidemiology
involves the study of group of people rather
than individuals.

5. Epidemiologist vs. clinician
A clinician identifies the ailment in his patients
using certain scientifically developed tools to
ascertain history of illness, clinical examination
and investigations.
Epidemiologist addresses the understanding
of the distribution and determinants of a
disease in a community (not an individual)
using standard parameters.

6. What constitute epidemiology
Epidemiology includes:-
1. The methods for measuring the health of
groups and determining the attributes
and exposures that influence health.
2. The study of the occurrence of disease in its natural habitat rather than in the controlled environment of the laboratory.

7. 3. The methods for the quantitative study of
the distribution, variation, and determinants
of health related outcomes in specific
groups (sub populations) of individuals, and
the application of this study to the
diagnosis, treatment, and prevention of
disease status or events.

8. Evolution of epidemiology
The evolution of medical sciences in its
earlier phase was based on curative
medicine. The primary objective was to cure
a patient of his illness. Doctors in historical
times looked at their patients as ill people
who needed some treatment.

9. Thus medical science was individual
oriented. But gradually it became evident
that better human health could be achieved
by prevention of diseases rather than by
cure.

10. A Historical Sketch A Long sketch of time ran for more than 2
millennia from Hippocrates ( B.C.) to
the first third of 19th century.
Hippocrates developed the medical
approach by providing concise, accurate and
complete description of actual clinical cases.

11. An Italian clinician called Bernardino
Ramazzini in 1700 moved from observation of
clinical cases to the consideration of ‘work
circumstances’ in similar cases. He is now
regarded as the founder of occupational
medicine. (Explained in his book. “De Morbis
Artificum Diatriba”).

12. The major step forward in epidemiology occurred in 1662
The major step forward in epidemiology occurred in John Graunt analyzed the weekly reports of births and deaths in London.
For the first time in the history, a quantified pattern of disease, deaths and births was Found. John Graunt is regarded as the founder of demography now.
His observations were published in his
book. Named “ the nature and political
observations made upon the bills of Mortality”.

13. After two centuries William Farr (1839) a
physician was given the responsibility for
medical statistics in England and Wales. He
set up a system for routine compilation of vital
statistics and application of data for evaluation
of deaths.

14. Hippocrates, Ramzinni, Graunt and Farr
contributed to the understanding of disease
frequency and distribution.
Another British physician John Snow
formulated and tested a hypothesis concerning
the origins of an epidemic of cholera in London
on the basis of available descriptive data.

15. Snow postulated that cholera was
transmitted by contaminated water. (then
unknown mechanism)
He observed that death rates from Cholera were particularly high in certain areas of London.
Those areas were supplied with water
by two water companies namely “Lambeth”
and “Southwark & Vauxhall” in Both the
companies that time drew water from river
Themes at a point heavily polluted with sewage.

16. The Lambeth company then changed its
source to an area of Themes where the water
was quite free from sewage of London.
The rate of cholera deaths then declined in
those areas suppied by Lambeth company.

17. Death rates from cholera According to water company supplying sub districts of London
Population in 1851
Cholera deaths in
Deaths per 100,000 living
Southwark and Vauxhall
Both companies
Lambeth
167, 654
301, 149
14, 632
192
182 00
114 60

18. Concepts of epidemiology
Definitions
“Epidemiology is defined as the study of the
distribution and determinants of health related
status or events in specified populations and
the application of this study to control the health
problems” (Last 1988)

19. Applications of epidemiology
The epidemiology is useful in:
1. Search of cause/causes of disease/diseases.
2. Helps to describe the health status of
population or groups.
3. Helps to discover and bridge gaps in
natural history of diseases.

20. 4. Helps in controlling the diseases. To break
the weakest link in chain of transmission of
communicable diseases and reducing non
communicable diseases.
5. Helps in planning of health programs on
evidence basis and setting up of health
priorities.
6. Helps to evaluate health programs and
interventions.

21. 7. Helps to determine the chances or
probability of occurrence of disease/
deaths and disability
8. Helps in better management of health
services and hospital services.
9. Helps to set-up cut-off levels between
normal and abnormal population and
establish trigger levels for action or
intervention.

22. Sources of epidemiological Measurements
1. Cross sectional surveys
2. Medical records
3. Death certificate
4. Census
5. Organizational data

23. Domains of epidemiology
Descriptive epidemiology
Descriptive epidemiology is the most Basic form of epidemiology. It is concerned with the description of the patterns of occurrence of health-related status or events in groups.
The determination of frequency and distribution of disease, incidence, prevalence, and mortality rates are included in descriptive epidemiology.

24. Analytical epidemiology
Analytical epidemiology is based on the
observations made in the descriptive
epidemiology. The design, execution and
analysis of subjects between groups helps
evaluate potential association between risk
factors and health outcomes to answer the
question “why?”.

25. Analytical epidemiology consists of two types of research processes
1. Observational process
2. Experimental studies

26. Basic triads of descriptive and analytical epidemiology
There are two different triads (3 essential
components) considered in studying different
sections

27. Descriptive epidemiology
Analytical epidemiology
Time (when)
Host
Place (where)
Agent
Person (who)
Environment

28. Triad of descriptive epidemiology
Time
Changing or stable
Seasonal variations
Secular trends (long-term study of
incidence)
Point source or propagated
Cyclical variations (spikes of
incidences at regular intervals)

29. Triad of descriptive epidemiology
Place
Geographically restricted or wide
spread
Relation to water and food supply
Multiple cluster involvement or one
Rural/Urban distribution

30. Triad of descriptive epidemiology
Person
Age
Socio economic status
Gender
Ethnicity / Race
Behavior

31. Triad of analytical epidemiology
Agent
Nutrients
Poisons
Allergens
Radiation
Physical trauma
Microbes
Psychological factors

32. Triad of analytical epidemiology
Host factors
Genetic factors
Immunologic state
Age
Personal behavior

33. Triad of analytical epidemiology
Environment
Overcrowding
Atmospheric changes
Modes of transmission
Vector
Vehicle
Reservoir

34. This forms the basis of clinical epidemiology.
When periodic observations are made over
a long period of time in patients with a wide
spectrum of clinical manifestations of the
disease, a complete profile of the natural
history of the disease may be obtained.
This forms the basis of clinical epidemiology.

35. Epidemiology of diseases
Sri Lanka is said to be facing a double
disease burden due to communicable and non
communicable diseases (NCD) today.
What is triple burden???

36. The diseases burden in the country is given in
terms of (apart from basic measures)
1.Years of potential life lost
2.Life expectancy free from disability
3. Disability adjusted life years lost – DALYs
4.Quality adjusted life years lost - QUALYs
loss per 1000 population.
Country has to fight to control communicable
and non communicable diseases.

37. Epidemiology of communicable diseases (CCD)
Definition :- Communicable disease
A communicable or infectious disease is an
illness caused by transmission of a specific
infectious agent or its toxic products from an
infected person or animal to a susceptible
host, either directly or indirectly through an
intermediate animal host, vector or inanimate
environment (Last 1995)

38. Disease Transmission
Man to man
Animal to man

39. What is an Epidemic? It is the occurrence of cases of illness,
specific health related behavior or other
health related events clearly in excess of
normal expectancy in a community or region.

40. An Endemic disease A disease that usually present in a
population or given area at a relatively high
prevalence and incidence rates in compared
to other areas.
E.g. Malaria is an endemic disease in
Polonnaruwa

41. Major emerging and re-emerging infectious diseases
1. HIV/AIDS
2. Hepatitis B and Hepatitis C
3. Tuberculosis
4. Dengue
5. Malaria
6. Japanese encephalitis
7. Plague
8. Cholera

42. Major reasons for emergence of infectious diseases
High population growth, uncontrolled and
unplanned urbanization,
Poor environmental sanitation,
Migration of population,
Natural disasters,
Growing international trade, tourism and rapid travel,
Alterations in microorganisms,
Resistance to antimicrobials,
Insecticide resistance,
Weak public health system.
Illiteracy and ignorance.

43. Chain of infection or chain of transmission
Infectious agent
Transmission process
Host
ENVIRONMENTS

44. Infectious agent
Pathogenicity
Virulence
Infectivity

45. Transmission process This is the second important link in the
chain of infection.
Transmission is defined as “Spread of
infectious agent through the environment or to
another person, from the reservoir and
source”.

46. Methods of transmission
Direct and
Indirect

47. Direct methods of transmission
Touching
Kissing
Sexual intercourse
Child birth
Breast-feeding
Air borne, short distance via droplets
(by coughing, Laughing, sneezing, spitting).
Transfusion of blood
Transplacental from mother to fetus

48. Indirect transmission
Vehicle borne transmission (by
contaminated food and water)
Vector borne transmission
Parenteral by unsafe injection
Fomite transmission
Unclean hands

49. Control of communicable diseases (CCD)-discuss under 5 headings
1. Control of infectious agents in the environments
2. Control of infectious agent in host
3. Control of outbreaks of CCD
4. Other measures
5. Specific measures for control of HIV epidemic

50. (1) Control of infectious agents in the environments
Controlling sources of infection
1. Supply of safe drinking water by treatment and chlorination of water, pasteurization of milk.
Safe disposal of human excreta and animal excreta by sewerage system and sanitary latrines, compost pits/manure pits.
3. Control vectors of diseases – by source reduction and anti-larval and anti-adult measures.
4. Animals – vaccinate dogs against rabies and eliminate street dogs.
5. Rodent control measures-trapping and killing
6. Hospital waste management
7. Disinfections

51. (2) Control of infectious agent in host
1. Reservoir control
2. Practice of chemoprophylaxis
3. Surveillance
4. Notification
5. Quarantine
1. Complete quarantine
2. Modified quarantine
6. Isolation
7. Education and behavior

52. Control of outbreaks of CCD-different steps will be discussed later
Communicable diseases like Malaria,
JE, DHF , Hepatitis E & A, Hepatitis B and
Diarrhoeal diseases quite often occur in
epidemic proportion. Many local and focal
outbreaks are being reported quite frequently;
Hence, control of outbreaks of these diseases
is an essential requirement.

53. (4) Other measures 1. Legislation Epidemic disease control act. And
notification helps control of CCD.
2. Observe international health
regulations

54. Notifiable diseases
Group A
Cholera
Plague
Yellow fever

55. Group B
Rubella
Diphtheria
Enteric fever
Food poisoning
Leptospirosis
Measles
Tuberculosis

56. Whooping cough
Acute anterior poliomyelitis
Simple continued fever of over seven days
Dengue
Dysentery
Encephalitis
Human rabies
Malaria
Tetanus
Typhus fever
Viral Hepatitis

60. Epidemiology of non-communicable diseases (NCD)
Non communicable diseases cover wide
range of heterogeneous conditions affecting
different organs and systems of different
socioeconomic groups.
Over the last two decades morbidity and
mortality due to cardiovascular diseases,
mental disorders, cancer and trauma have
been rising due to following causes.

61. Causes 1. Rise in life expectancy and increasing
number of senior citizens.
2. Changing life styles: Faulty diet, use of
alcohol, sedentary life-physical inactivity
and rising stress-leading to obesity and
stress related problems.

62. 3. Exposure to environmental risk factors-air
pollution.
4. Use of tobacco
5. Increasing population and rise in
automobiles and trauma incidence.

63. Implications In view of the chronic morbidity and high
cost involve in the management of non-
communicable diseases attention need to be
focused on prevention, early detection and
appropriate management. Further, these
diseases cause lot of disability and
dependency and disease burden.

64. Multi - factorial origin
Causes of NCD are multi-factorial. Range
of life styles: risk taking behavior, changing
dietary pattern, physical inactivity, use of
alcohol and tobacco and stress in life have
been incriminated.

65. Future For non-communicable diseases throughout
the all levels of care so as to reduce morbidity
and mortality.

66. 1. Well-structured information education and
communication for primary and secondary
prevention of NCD.
2. Reorientation and skill up gradation of
health care providers

67. 3. Establishment of Referral linkages between
primary secondary and tertiary institution.
4. Production and provision of drugs for NCD.
5. Development of institution for rehabilitation
of disabled persons due to NCD, teaching
persons to live with their disability.

68. 6. Development of hospices for terminally ill
people who cannot have home based care.
7. Creation of epidemiological database on
NCD especially, CVD’s, strokes and
diabetes.