1. GENERAL EPIDEMIOLOGY - 1 BY Dr. HIDAYATHULLA SHAIKH,

2. At the end of lecture student should bw able to -
Contents
At the end of lecture student should bw able to -
Know Introduction
Tell History of epidemiology
Mention Aims
Enumerate Epidemiology v/s clinical medicine
Mention Principles of epidemiology
Discuss Descriptive epidemiology

3. what, when, why, how, where & who.
INTRODUCTION
I keep six honest serving men, they taught me all I know. Their names are –
what, when, why, how, where & who.
ever since the beginning of this universe mankind has struggled constantly either directly or indirectly against diseases.
When attempts are made to understand the cause of the diseases, two general approaches may be considered.
The first deals with the identification and tracing of the agent of the disease after it has entered or affected the individual host & second is his environment.

4. The word EPIDEMIOLOGY is derived from the Greek word, Epidemic,
Epi = upon,
demos = people,
logos = science or study.

5. Who is an epidemiologist?
Any person who researches into occurrence of disease or disability in groups of people is called an epidemiologist.
QUALIFICATIONS OF AN EPIDEMIOLOGIST (SMILLIE):
Familiar with statistical techniques
Well grounded in diagnosis of disease
Thorough with medicine, relating to epidemics
Good knowledge of bacteriology, immunology and physiology
Knowledge of principles of preventive medicine

6. HISTORY
Hippocrates(460 – 375 BC ) was the first known epidemiologist.
“No disease is sent by evils or demons, but is the result of natural causes”-
Thomas syndenham ( ): wrote the history of disease and became the “founder of epidemiology”.
John snow ( ): is considered the
“father of epidemiology” he found the epidemic of cholera in London, in august 1854.

7. DEFINITION OF EPIDEMIOLOGY
JOHN M LAST (1988)
“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 health problems.”

8. Components of epidemiology
Frequency
Essential for comparing disease frequency in different populations or sub groups of the same population to suspect causal factors.
Distribution
Distribution patterns by time, place & person.
Here the epidemiologist examines whether there has been increase or decrease of disease over a time span, in which geographical area, in males or females, which age group etc.
Determinants
A unique feature of epidemiology is to test etiological hypothesis and identify the underlying causes or risk factors

9. Aims of epidemiology
To describe the magnitude and distribution of the disease problem in human populations.
To provide data essential for planning, implementation, and evaluation of health services and setting priorities among the services.
To identify risk factor or etiological agents.
To eliminate or reduce the health problem or its consequences and
To promote the health and well being of society as a whole.

10. EPIDEMIOLOGY CLINICAL MEDICINE SL NO 1.
Unit of study defined population.
Individual/case. 2.
Relevant data, identifies sources of infection, mode of spread, determines future trends & control measures.
Case, diagnosis, prognosis, prescribes treatment. 3.
Concerned with those who are sick & those who are healthy
Often concerned with those who are sick. 4.
Investigator goes to community
Patients comes to doctor 5.
Conceptual, results in the form of tables & graphs.
Based on biomedical concepts, refining tech..of diagnosis & treatment.

11. Principles of epidemiology
Exact observation
Correct interpretation
Rationale explanation
Scientific construction

12. Methods of epidemiology

14. Descriptive epidemiology
First phase of epidemiological investigation
The various procedures involved.
Defining the population to be studied
Defining the disease under study
Describing the disease by
Time
Place
person
Measurement of disease
Comparing with known indices
Formulation of an etiological hypothesis

15. Defining the population to be studied.
Investigation of populations not individuals.
It can be a whole population in the geographic area or more often a representative sample.
Can also be specially selected as sex groups, occupational groups, hospital patients etc.
Defined population should be large enough.
The community chosen should be stable, without migration in or out of the area.

16. Defining the disease under study.
Disease definition should be precise and valid
Operational definition, definition by which the disease or condition can be identified and measured in the defined population with degree of accuracy.

17. Ex tonsillitis mighty be defined as the inflammation of the tonsils by infection usually by streptococcus pyogenes. But this can not be used to measure disease in the community.
So the operational definition spells out which includes with the above definition. Presence of enlarged and red tonsils with white exudate which on throat swab culture grows predominantly S. pyogenes.
Sometimes epidemiologist frames his own definition.
keeping objectives in mind.

18. Describing the disease under study
Time
Place
Person
Year
Season
Month
Week
Day
Hour of onset
Duration
Climatic zone
Country
Urban/ rural
Local community
Towns
Cities
Institutions
Age
Sex
Marital state
Occupation
Social status
Education
Birth order
Family size
Height
Weight
Blood pressure
Blood cholesterol
Personal habits

19. Time distribution:
Three kinds of time trends or fluctuations in disease occurrence.
1) Short term fluctuation
2) Periodic fluctuations and
3) Long term fluctuation.

20. Place distribution, (geographical comparision)
Important dimension of descriptive epidemiology.
Genes vs. environment, changes with migration, possible roles of diet and other etiological factors
Variations may be classified as:
International variation
National variation
Rural and urban differences
Local distributions
Migration studies

21. International variations
Descriptive studies by place have shown that the pattern of disease is not similar every where.
Ex we know that cancer exist all over the world however there is the marked difference in the incidence of each cancer in the different parts of the world.
Ex; cancer of the stomach is very common in Japan but unusual in US ,
cancer of oral cavity is exceedingly common in india than other countries,
International study of breast cancer shows the rates differ widely from country to country, with lowest prevalence in Japan and highest in western countries.

22. National variation
It is obvious that variations in disease occurrence must also exist within the countries or national boundaries.
Ex, the distribution of endemic goiter, fluorosis, leprosy, malaria etc have all shown their variation in distribution in India.
So one of the function of the descriptive epidemiology is to provide the data regarding the type of disease problems, & their magnitude in terms of incidence, prevalence, mortality rates.
Such information is needed to demarcate the affected areas & for providing appropriate health care services.

23. Rural – urban variations
Chronic bronchitis, accidents, lung cancer, cardio vascular diseases, mental illness are usually more common in urban areas.
On the other hand skin diseases, zoonotic diseases, soil transmitted helminthes are more common on rural areas.
The epidemiologist seeks to define groups at the higher risk for particular disease and provides guidelines to the health administrator for their prevention and control.

24. Local distributions
Inner and outer city variations are well known. These variations are best studied with the aid of spot maps or shaded maps.
These maps show at glance the areas of high and low frequency, the boundaries and pattern of disease distribution.
If the map shows the clustering of cases, it may suggest a common source of or a common risk factor shared by all the cases.
It was by such study JOHN SNOW in 1854 investigated cholera epidemic in the broad street, golden square district, London.

25. Snow’s findings

26. Migration studies
Large scale migration of human populations from one country to another provides a unique opportunity to evaluate the role of possible genetic and environmental factors in the occurrence of disease in the population.
Migrants studies can be carried in two ways.
Comparison of disease & death rates with migrants with those of their kin who have stayed at home.
This permits study of genetically similar groups but living under different environmental conditions or exposures.

27. b) Comparison of migrants with local population of the host country, & this provides information on genetically different groups living in similar environment
Migrant studies have shown that men of Japanese ancestry living in USA experience a higher rate of coronary heart disease than do the Japanese in Japan.
Ex Japan has a higher rate of stomach cancer and lower rate of colon cancer than the US has, however the 3rd generation descendents of Japanese immigrants to USA have rates of stomach and colon cancer similar to rate of total US population.

28. Person distribution The development of disease by age, sex,
occupation,
marital status,
behavior and stress
social class and other host factors.

29. Morbidity 4). Measurement of disease Incidence Prevalence
Cross sectional
Longitudinal studies

30. Cross sectional studies
Simplest form of an observational study, also called as prevalence study.
It is based on a single examination of a cross section of a population at one point in time.
The results which can be projected on the whole population provided the sampling is done correctly.
Cross sectional studies are more useful for chronic diseases than short lived diseases.

31. Ex in a study of hypertension, one can also collect data during the survey about age , sex, physical exercise, body weight, salt intake, etc.
Thus one can determine how prevention of hypertension is related to certain variables simultaneously measured,
Such a study tells us about the distribution of the disease in a population rather than its etiology & incidence.

32. Longitudinal studies
These are useful in
To study the natural history of the disease and its future outcome.
For identifying the risk factors of the disease.
For finding out incidence rate or rate of occurrence of new cases of disease in the community.
Longitudinal studies provide valuable information which the cross sectional studies may not provide.
But longitudinal; studies are difficult to organize and more time consuming than cross sectional.
Measurements can also be extended to health states and events.
ex study of blood pressure levels in population will reveal the normal values rather than abnormal ones related to the disease.

33. 5) Comparing with known indices
Comparison between different populations, groups, sub groups, it is possible to arrive at clues to disease etiology.
Risk groups can be identified .

34. 6. Formulation of hypothesis
Hypothesis: is a supposition, arrived at from observation or reflection. It can be accepted or rejected, using the techniques of analytical epidemiology.
A hypothesis should specify:
Population
Specific cause being considered
The expected out come – disease
Dose – response relation ship – the amount of cause needed to lead to a stated incidence effect.
The time response relation ship.

35. Uses of descriptive studies
Data pertaining to morbidity and mortality of communities.
Provide clues to etiology & help in formulating the etiological hypothesis.
Provide background data for planning, organizing and evaluating health services.
Contribute to research by describing variations in disease occurrence by time, place and person.