The document provides an introduction to epidemiology, detailing the objectives and foundational concepts, including its historical context and the evolution of the field. It defines epidemiology as the study of health-related states in populations to inform prevention and control measures. The document also outlines the levels of disease prevention and the significance of understanding disease patterns and transmission dynamics.

1. INTRODUCTION TO
EPIDEMIOLOGY
DR. PENIAS TEMBO (MD)
(MPH.MBChB,BSc HB,Dip
Med,Cert TM)

2. EPIDEMIOLOGY
• Objectives
• At the end of the course, students should be
able to demonstrate knowledge of:
• describe the nature and main uses of
epidemiology
• the epidemiology approach to defining and
measuring the occurrence of health related
states in population

3. • In addition, students are expected to have gained a
variety of skills, including ability to:
describe the common cause of death, disease
and disability in their respective communities
 outline appropriate study designs to answer
specific questions concerning disease causation,
natural history prognosis, prevention and
evaluation of therapy and other interventions to
prevent and control disease

4. WHAT IS EPIDEMIOLOGY
Key messages (Things to remember)
• Epidemiology is a fundamental science of
public health
• Epidemiology has made major contributions to
improving population health
• Epidemiology is essential to the process of
identifying and mapping emerging diseases

5. Historical context
Origins
• Epidemiology’s roots are nearly 2500 years old.
• Epidemiology originates from Hippocrates observations more
than 2000 years ago that environmental factors influence the
occurrence of disease.
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6. • Circa 400 B.C.
Hippocrates attempted to explain disease
occurrence from a rational rather than a
supernatural viewpoint. In his essay entitled
“On Airs, Waters, and Places,”
• Hippocrates suggested that environmental and
host factors such as behaviors might influence the
development of disease.

7. • 1662
Another early contributor to epidemiology
was John Graunt, a London haberdasher and
councilman who published a landmark
analysis of mortality data in 1662.

8. • This publication was the first to quantify
patterns of birth, death, and disease
occurrence, noting disparities between males
and females, high infant mortality,
urban/rural differences, and seasonal
variations.

9. • 1800
William Farr built upon Graunt’s work by
systematically collecting
and analyzing Britain’s mortality statistics.
• Farr, considered the father of modern vital statistics
and surveillance, developed many
of the basic practices used today in vital statistics
and disease classification

10. • He concentrated his efforts on collecting vital
statistics, assembling and evaluating those
data, and reporting to responsible health
authorities and the general public.

11. • However, it was not until the 19th
Century that the distribution of disease
in specific human population groups
was measured to any large extent.
• This wok not only marked the formal
beginnings of epidemiology but also
Some of its most spectacular achievements

12. • The findings by John snow that the risk of
cholera in London was related to the drinking
water supplied by a particular company
provides a well-known example
• Snow’s epidemiology studies were one aspect
of a wide ranging series of investigations that
examined related physical, chemical,
biological, sociological and political processes.

13. • Comparing rates of disease in subgroups of the
human population became common practice in
the late C19th
and early C20th
.
• This approach was initially applied to the control
of communicable diseases but proved to be useful
way of linking environmental conditions or
agents to specific diseases.
• In the second half of the twentieth century,

14. These methods were applied to chronic non
communicable diseases such as heart diseases
and cancer, especially in the middle and high-
income countries.

15. Recent developments in Epidemiology
• Epidemiology in modern form is a relatively
new discipline and uses quantitative methods
to study diseases in human populations, to
form prevention and control efforts.e.g.
Richard Doll and Andrew Hill studied the
relation between tobacco use and lung cancer
beginning in the 1950s.

16. • In the 1980s, epidemiology was extended to
the studies of injuries and violence.
• In the 1990s, the related fields of molecular and
genetic epidemiology (expansion of
epidemiology to look at specific pathways,
molecules and genes that influence risk of
developing disease) took root.

17. • Beginning in the 1990s and accelerating after
the terrorist attacks of September 11, 2001,
epidemiologists have had to consider not only
natural transmission of infectious organisms
but also deliberate spread through biologic
warfare and bioterrorism.

18. Definition of Epidemiology
• The word “epidemiology “ is derived from
Greek words: epi:“ upon”,demo “people”
lagos“study”

19. • Epidemiology as defined by Last is’ the study
of the distribution and determinants of
health- related states or events in a specified
population, and the application of the study to
the prevention and control of health
problems.

20. • This broad definition of epidemiology can be
further elaborated as follows;
• Study: includes-surveillance, observations,
hypothesis testing, analytic research and
experiments
• Distribution: refers to frequency and
pattern of occurrence of disease analysis

21. • Frequency refers not only to the number of
health events such as the number of cases of
meningitis or diabetes in a population, but
also to the relationship of that number to the
size of the population.

22. • The resulting rate allows epidemiologists to
compare disease occurrence across different
populations

23. • Pattern refers to the occurrence of health-
related events by:
 time
 place
 person.

24. • Time patterns may be :
Annual
 seasonal
 weekly
Daily
 hourly,
 weekday versus weekend, or any other breakdown
of time that may influence disease or injury
occurrence.

25. • Place patterns include:
 geographic variation,
 urban/rural differences
 and location of work sites or schools.

26. • Personal characteristics include demographic
factors which may be related to risk of illness,
injury, or disability such as age, sex, marital
status, and socioeconomic status, as well as
behaviors and environmental exposures.

27. • Determinants :includes factors that influence
health-biological, chemical, physical, socioal,
cultural, economic, genetic and behavioural.
• Health related states and events: refers to –
diseases, causes of death,behaviours such as
use of tobacco, positive health status, reaction
to preventive regimes and provision and use
of health services

28. • Specified population: include those with
identifiable characteristics, such as
occupational groups.
• Application to prevention and control-The
aims of public health- to promote, protect and
restore health.

29. Concerns of Epidemiology
• Epidemiologists are concerned not only with
deaths, illnesses and disability, but also with
more positive health states and most
importantly with the means to improve health
• The term ‘disease ‘encompasses all
unfavorable health changes, including injuries
and mental health.

30. Uses of epidemiology
• Assessing the community’s health
• Making individual decisions
• Completing the clinical picture
• Searching for causes-to searching for causal
factors that influence one’s risk of disease

31. Epidemiological approach
• The epidemiological approach to problems of
health and disease is based on two major
foundation
Ask questions and getting answers that lead to
further questions
Making comparisons and draw inferences

32. Questions related To health events
• What is the event(problem)?
• What is the magnitude?
• Where did it happen?
• When did it happen?
• Who are affected?
• Why did it happen/

33. Questions Related to Health Action
• What can be done to reduce this problem and
it’s consequences?
• How can it be prevented in the future?
• What action should be taken by the
community ?
• Who should carry out these activities?
Health services, other sectors, where and for
whom these activities be carried out?

34. • What resources are required?
• How are these activities be organized?
• What difficult may arise, and how might they
be overcomed?

35. EPIDEMIOLOGY &CLINICAL MEDICINE
EPIDEMIOLOGY
• Population as unit of study
• Concerned with disease
pattern in the entire
population
• Epidemiologists confronted
with relevant data derived
fro particular epidemiological
study-to identify a particular
source of infection, mode of
spread,
CLINICAL MEDICINE
• Cases/ case with a disease as
unity of study
• Physician is concerned with
disease in a individual patients
• Concerned with both the sick
and the healthy
• Physicians seeks diagnosis
from which he derives a
prognosis and prescribes
specific treatment

36. Epidemiology
or an etiological factor in order
to determine a future trend
and recommend specific
control measures
• Epidemiologist evaluates the
outcome of preventive and
therapeutic measures
instituted which provides the
necessary guidance and feed-
back to the health care
administrator for effective
Clinical Medicine
• Patient comes to a doctor
• Is based on biomedical
concepts with an ever-
increasing concern for
refining the technique of
diagnosis and treatment at
individual level

37. Epidemiology
Management of public health
programmes
• The investigator goes to the
community to find persons
who have a disease or
experience of the suspected
causal factor in question
Clinical Medicine
• The subject matter is easily
“perceived “by such
techniques as clinical and
laboratory examination ,
postmortem reports

38. • Clinical medicine and epidemiology are not
antagonistic.
• Both are closely related, co-existent and
mutually helpful
• Epidemiological enquiries depends on
appropriate clinical considerations such as how
the disease in question can be identified among
individuals comprising the group under scrutiny

39. • Likewise, a knowledge of prevalence and
prognosis derived from epidemiological
research is important to the clinician for the
diagnosis and management of individual
patients and their families

40. NATURAL HISTORY OF A DISEASE
• Definition-Natural history of a disease refers
to systematic description of the course of
disease over time, un affected by treatment.
(The course and outcome of disease in
individuals and groups)

41. Cont
Good
Health
Subclinical
Changes
Clinical
changes
DEATH
RECOVERY

42. • During the susceptible phase, risk factors are
only present or there is accumulation of
factors sufficient for the disease process to
begin in a susceptible host.

43. • During the preclinical or pre symptomatic
phase, pathological changes of the disease has
started.
• extending from the time of exposure to onset of
disease symptoms, is usually called:
The incubation period for infectious diseases
 the latency period for chronic diseases.
• There are some physical manifestations, but NO
obvious disease is present

44. This period may be as brief as seconds for
hypersensitivity and toxic reactions to as long as
decades for certain chronic diseases.
 The onset of symptoms marks the transition from
subclinical to clinical disease.
• In the clinical disease phase, signs and symptoms of
diseases are present.

45. • In some people, however, the disease process may
never progress to clinically apparent illness.
• In others, the disease process may result in illness
that ranges from mild to severe or fatal.
• This range is called the spectrum of disease.
• Ultimately, the disease process ends either in
recovery, disability or death

46. Chain of infection
• According to traditional triad model, it holds
that infectious diseases result from the
interaction of :
Agent
Host
 environment

47. • 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.

48. • Reservoir
The reservoir of an infectious agent is the habitat in which the
agent normally lives, grows and multiplies.
• Reservoirs include:
 Human –transmission of person to person(mumps, chicken pox)
 Animals reservoirs (vertebrae animals to human (beings
zoonosis -plague)
 Environment reservoirs( Plants, soil, and water)

49. • Portal of exit
Portal of exit is the path by which a pathogen
leaves its host.
 The portal of exit usually corresponds to the site
where the pathogen is localized. For example:
- influenza viruses and Mycobacterium tuberculosis
exit the respiratory tract
- schistosomes through urine
- cholera vibrios in feces

50. - Sarcoptes scabiei in scabies skin lesions
- enterovirus 70, a cause of hemorrhagic conjunctivitis,
in conjunctival secretions
- Some bloodborne agents can exit by crossing the
placenta from mother to fetus (rubella, syphilis,
toxoplasmosis),
- while others exit through cuts or needles in the skin
(hepatitis B) or blood-sucking arthropods (malaria).

51. Mode of transmission: An infectious agent may be
transmitted from its natural reservoir to a susceptible host in
different ways
• Direct
-direct contact(skin to skin, kissing and sexual intercourse
− droplet spread(refers to spray with relatively large,
short-range aerosols produced by sneezing, coughing, or
even talking.e.g. Pertussis and meningococcal)

52. • Indirect
− Air borne through dust or droplet nuclei
suspended in the air( measles virus)
− Vehicle borne can be contaminated by
contaminated food, water, biologic products
(blood), and fomites (inanimate objects such as
handkerchiefs, bedding, or surgical scalpels).

53. − Vectorborne (mechanical or biologic)
mosquitoes, fleas, and ticks may carry an
infectious agent through purely mechanical
means or may support growth or changes in the
agent

54. • Port of entry
The portal of entry refers to the manner in which a
pathogen enters a susceptible host
The portal of entry must provide access to tissues in
which the pathogen can multiply or a toxin can act.
Often, infectious agents use the same portal to enter
a new host that they used to exit the source host.

55. *Knowledge of chain of infection is important as
put Interventions that are directed
at:
-Controlling or eliminating agent at source of
transmission
- Protecting portals of entry
- Increasing host’s defenses

56. Factors which can influence the
development of disease are:
• Strain of agent
• Dose of agent
• Route of infection
• Host characteristics
• Treatment

57. Levels of disease prevention
• Primary prevention of a disease
These are actions that removes the possibility
that a disease will occur. Actions precedes
disease or dysfunction(the individuals
/population are health)
Generalized health promotion and specific
protection against diseases
The activities are both preventive and promotive

58. Examples of primary prevation
• Health education about accidents and
poisoning prevention,standared of nutrition
and growth and development for each stage of
life, exercise requirements ,stress management
,protection against occupational hazards,etc
• Immunizations
• Risk assessment for disease

59. • Family planning services and marriage
counseling
• Environmental sanitation and provision of
adequate housing,recreation,and work
conditions
• Removal of any noxious Agents (Toxic
agents)in the environment or any agents in the
environment that would cause disease-refuse
disposal.

60. • Preventing agents from being in contact with
the host e.g., mosquito nets- to prevent
infected mosquitoes.

61. Secondary prevention
• This is pre clinical / clinical disease stage.
• It emphasize on early detection/ diagnosis,
prompt treatment/ intervention and health
maintenance for individuals experiencing health
problems.
• Measures are aimed at people who have a disease.
• It includes, prevention of progression of a clinical
disease( halt),prevention of complications and
disabilities.

62. • Reduces disease prevalence
• Level of curative stage to prevent
disability( happens in district hospitals )

63. Examples of secondary prevention
• Screening surveys- DHS-R.P.R
• Screening tests e.g. early screening and
treatment for T.B. to prevent chronocity.
Stool for m/c/s to rule out worms.
• Encouraging medical and dental check ups
• Teaching self - examination for breast and
testicular cancer

64. Tertiary prevention
• This is the level of disability limitation and
rehabilitation .
• It begins after an illness, when a defect or
disability is fixed, stabilized , or irreversible .
• Usually a point of NO RETURN
• Its focus is to help rehabilitate individuals and
restore them optimum level of functioning within
the constraints of disability to try to prevent

65. • Hopelessness
• Helplessness
• Workelessness
• Dependence
• Suicidal tendencies

66. Examples of tertiary prevention
• Should be helped or request help from clubs
• Referring a client who has had a colostomy to a
support group
• Use of prosthesis for amputees and also change
hobbies e.g. from golfer to dart player
• Palliative care of terminally ill patients to prevent
undignified or painful death
• Rehabilitation by- Retraining remaining capacities-
retrain maximal independence including employment.