Basic introduction about Epidemiology

1. Introduction to
epidemiology

2. Definition of epidemiology
“The study of the distribution & the determinants of health related states or
events in specified population, and the application of this study to the control
of health problems”
(Greek; Epi = upon, Demos = populations, Logos = scientific
study).

3. Components of epidemiology
3 Ds
Disease
frequency
Determinants
of disease
Distribution
of disease

4. 1)Disease frequency
• Measurement frequency of disease, disability or death & summarizing in the
form of rate & ratio ( e.g. prevalence rate, incidence rate, death rate)
• Rate & ratio are essential for comparing disease frequency in different
populations
• Important in the development of of strategies for prevention or control of
health problems

5. 2)Distribution of disease
• An important function of epidemiology is to study the distribution of
diseases in a population by time , place & person
• To examine whether there has been an increase or decrease of disease over
time span or higher concentration of disease in one geographic are than in
others
• Whether the disease occurs more often in men or in particular age group.

6. 3)Determinants of disease
• A unique feature of epidemiology is to test aetiological hypotheses & identify
the underlying causes or risk factor of disease
• This aspect called analytical epidemiology

7. Aims of epidemiology
1. To describe the distribution and magnitude of health & disease problems in
human populations.
2. To identify aetiological factors ( risk factors) in the pathogeneses of
diseases
3. To provide essential data to the planning , implementation and evolution of
services for the prevention , control, and treatment of disease and to the
setting up of priorities among those services

8. Epidemiological approach
1. Asking questions
2. Making comparisons

9. Asking questions
“ a means of learning or asking questions… and getting answers
that lead to further questions.
a) Related to health events
b) Related to health actions

10. a) Related to health events
1. What is the event?
2. What is its magnitude?
3. Where did it happen?
4. Who are affected ?
5. Why did it happen ?

11. b) Related to health actions
1. What can be done to reduce this problem and its consequences?
2. How can it be prevented in the future ?
3. What action should be taken by the community ?by the health services?
By other sectors? Where & for whom theses activities be carried out ?
4. What resources are required ? How are the activities be organized ?
5. What difficulties may arise , and how might they be overcome ?

12. Making comparisons
• Comparison of 2 or more groups ( or individuals) 1 group having
the disease ( or exposed to risk factor) & the other group not
having the disease( or not exposed to risk factors)
• Make sure the study & control groups should be similar with
regard to their age & sex & other variables.

13. Uses of epidemiology
1. In Health Care Management
2. In Understanding the disease process
3. In Public Health Practice
4. In Clinical and preventive practice

14. 1)In Health Care Management
• Making Community Diagnosis
• Planning & Evaluation of Health Services
• Developing Health Policies

15. 2. Understanding Disease Process
• Studying natural history of diseases
• Searching for Causes & Risk factors
• Historic studies of rise and fall of diseases
• Identification of Syndromes

16. 3. Uses in Public health practice
• Investigations of Epidemics
• Surveillance for Diseases
• Making Projections for Future
• Disease Screening Programmes
• Formulating medical teaching curricula

17. 4. Assisting in Clinical Practice
• Assessing Effectiveness of Treatment Modalities
• Assessing Effectiveness of Preventive modalities
• Studying Prognostic factors
• Studying Effectiveness of diagnostic Modalities
• Assisting in Clinical decision making

18. What is ‘Health’ ?
• Oxford dictionary
State of being well in body or mind

19. • “Health is a state of complete physical, mental and social well-
being and not merely the absence of disease or Infirmity.”
W.H.O. Definition of Health

20. Concept of Disease

21. Disease
• Oxford English Dictionary – the condition of body or some
part of organ of body in which its functions are disrupted or
deranged.
• Simplest definition – ‘Opposite to Health’.
• Disease is a physiological/psychological dysfunction.

24. The Triangle of Epidemiology

25. Agent Factors
•What are the “Types of agent factors”
???

26. Host Factors
1.Demographic characteristic ( age, sex, ethnicity)
2.Biological characteristic ( genetic factors, blood group,
cholesterol in the blood)
3.Social & economic characteristic ( socio-economic status,
education, occupation, stress, housing)
4.Lifestyle factors (living habits, nutrition, smoking, physical
exercise )

27. 3) Environmental factors
• Environment is classified as “internal” and “external”.
• Internal : each & every component part, every tissue, organ & organ
system & their harmonious functioning within the system
• External: all that which is external to the individual human host.
• It can be divided into physical, biological and psychosocial
components.e.g eating habits, life style & personal habits

30. Natural history of disease

31. Natural History of Disease
• It is the progression of a disease process in an
individual over time, in the absence of treatment.
• The time frame of disease may vary from individual to
individual.

32. Stage of susceptibility
• The process begins with the appropriate exposure to the factors.
• For an infectious disease, the exposure is a microorganism.
• For cancer, the exposure may be tobacco smoke (for lung cancer)

33. Stage of subclinical disease
• pathological changes occur without the individual being aware of
them.
• extending from the time of exposure to onset of disease symptoms,
• called the incubation period (infectious diseases) & the latency
period (chronic diseases).
• Disease is asymptomatic (no symptoms)
• Incubation periods of varying from minutes to decades .

34. Exposure Clinical Effect Incubation/Latency Period
Salmonella Diarrhea, often with fever and
cramps
6–48 hr
Hepatitis A virus Hepatitis 14–50 days, average 4 weeks
Hepatitis B virus Hepatitis 50–180 days, usually 2–3 m
Human immunodeficiency virus AIDS <1 to 15+ years

35. • Although disease is not apparent during I.P, pathologic changes
may be detectable with laboratory, radiographic, or other
screening methods.
• Intervention at this early stage is more effective than treatment
given after the disease has progressed and become
symptomatic

36. Stage of clinical disease.
• The onset of symptoms marks the transition from subclinical to clinical
disease.
• Most diagnoses are made during the stage of clinical disease.
• The disease process ends either in recovery, disability or death