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- 1.
- 2. Introduction of epidemiology TheGreek physician Hippocrates is sometimes said to be the father of epidemiology. He is the first person known to have examined the relationships between the occurrence of disease and environmental influences. • epi – means “on, upon, befall” • demo – means “people, population, man” • logy – means study
- 3. Definition of Epidemiology:- Thestudy of frequency, distribution and determinants of diseases is known as epidemiology. (International epidemiological association)
- 4. Key Words ofEpidemiology • Epidemic : ( Epi = upon : demos = people ) An outbreak of disease in a community in excess of “normal expectation ” • Endemic: (en = in; demos = people). The constant presence of disease within a geographic area or the usual prevalence of a given disease in a particular area. malaria, tuberculosis, etc. • Pandemic: (pan = all: demos = people) An epidemic which spreads from country to country or over the whole world, as for example, the recent epidemic of AIDS.
- 5. Aims of Epidemiology •Todescribe the distribution and size of disease problems in human population. • To identify etiological factors in the pathogenesis of disease. • To provide data essential to the planning, implementation, and evaluation of services for the prevention, control and treatment disease and to setting up the priorities among these services.
- 6. Uses of Epidemiology •Tostudy the effects of disease state in a population over a time and predict future health. • To diagnose the health of the community. • To evaluate health services. • To estimate the individual risk from group experiences. •To identify the syndrome. •To search for causes of disease.
- 7. Levels of Prevention •Primaryprevention Health promotion Specific protection •Secondary prevention Early diagnosis (screening tests, case finding programmes ) Adequate treatment •Tertiary prevention Disability limitation Rehabilitation – Functional rehabilitation – Vocational rehabilitation – Social rehabilitation – Psychological rehabilitation
- 8. Epidemiological approach 1. Askingquestions 2. Making comparisons 1. Asking questions Epidemiology has been defined as a means of learning or asking questions.. and getting answers that lead to further questions RELATED TO HEALTH EVENTS •What is the event? (the problem) •Where did it happen? •When did it happen? •Who are affected? •Why did it happen?
- 9. Conti.. RELATED TO HEALTHACTIONS •What can be done to reduce this problem and its consequences ? •How can it be prevented In the future ? •What action should be taken by the community ? By the health services? By other sectors ? •What resources are required ? How are the activities to be organized ?
- 10. 2. Making comparisons •Thisapproach is to make comparisons and draw inferences. •Comparison may be made between different population at a given time eg. Rural with urban population •Between sub group of population eg. Male with female population •Between various periods of observation eg. Different seasons Conti..
- 11. Tools of measurement 1.Rates 2. Ratios 3. Proportions 1. Rates A rate measures the occurrence of some particular event (development of disease or the occurrence of death) in a population during a given time period. Number of deaths in one year Death rate = X 1000 Mid - year population
- 12. (1) Crude rates:These are the actual observed rates such as the birth and death rates. Crude rates are also known as unstandardized rates. (2) Specific rates: These are the actual observed rates due to specific causes (e.g., tuberculosis); or occurring in specific groups (e.g., age-sex groups) or during specific time periods (e.g.. annual, monthly or weekly rates). (3) Standardized rates: These are obtained by direct or indirect method of standardization or adjustment, e.g., age and sex standardized rates. Conti..
- 13. 2.RATIO Another measure ofdisease frequency is a ratio. It expresses a relation in size between two random quantities. examples include: •The number of children with malnutrition at a certain time • sex-ratio, doctor population ratio, child woman ratio, etc Conti..
- 14. 3.PROPORTION A proportion isa ratio which indicates the relation in magnitude of a part of the whole. The numerator is always included in the denominator. A proportion is usually expressed as a percentage. The number of children with scabies at a certain time Example x 100 The total number of children in the village at the same time Conti..
- 15. MORTALITY The occurrence ofdeath in a population. Mortality data are relatively easy to obtain, and, in many countries, reasonably accurate. Many countries have routine systems for collecting mortality data each year, information on deaths is analyzed and the resulting tabulations are made available by each government.
- 16. Limitations of mortalitydata • Incomplete reporting of deaths • Lack of accuracy:-inaccuracies in the recording of age and cause of death • Lack of uniformity:- There is no uniform and standardized method of collection of data • Changing:- Changing coding systems and changing fashions in diagnosis may affect the validity. • Diseases with low fatality:-the disease is associated with low fatality (e.g., mental diseases, arthritis).
- 17. MORTALITY RATES ANDRATIOS 1. Crude death rate The simplest measure of mortality is the crude death rate It is defined as the number of deaths (from all causes) per 1000 estimated mid-year population in one year, in a given place. Number of deaths during the year = X 1000 Mid-year population
- 18. 2. Specific deathrates When analysis is planned to throw light on aetiology, it is essential to use Specific death rates. The specific death rates may be (a) cause or disease specific e.g., tuberculosis cancer, accident; (b) related to specific groups e.g. age-specific, sex-specific , age and sex specific, etc. Conti..
- 19. 3. Case fatalityrate (Ratio) Case fatality rate represents the killing power of a disease.it is simply the ratio of deaths to cases. The time interval is not specified. Case fatality rate is typically used in acute infectious diseases (e.g., food poisoning, cholera, measles) Total number of deaths due to a particular disease = X 100 Total number of cases due to the same disease Conti..
- 20. 4. Proportional mortalityrate (Ratio) •It is sometimes useful to know what proportion of total deaths are due to a particular cause (e.g.. cancer) or •what proportion of deaths are occurring in a particular age group (e.g., above the age of 50 years). •Proportional mortality rats expresses the number of deaths due to a particular cause (at in a specific age group) per 100 (or 1000) total deaths. Thus we have: Conti..
- 21. (a) Proportional mortalityfrom a specific disease Number of deaths from the specific disease in a year = X 100 Total deaths from all causes in the year Conti..
- 22. 2. Under 5proportionate mortality rate Number of deaths under 5 years of age in the given year. = X 100 Total number of deaths during the same period 3. Proportional mortality rate for aged 50 years and above Number of deaths at persons aged 50 years and above = X 100 Total deaths at all age groups in that year Conti..
- 23. 5.Survival rate It isthe proportion of survivors in a group, (e.g. of patients) studied and followed over a period tag, a 5 year period. Survival rates have received special attention in cancer studies. Total number of patients alive after 5 years Survival rate =X 100 Total number of patients diagnosed or treated Conti..
- 24. MORBIDITY The occurrence ofan illness or illnesses in a population. Morbidity has been defined as any departure, subjective or objective, from a state of physiological well-being. The term is used equivalent to such terms as sickness. illness, disability etc. WHO Expert Committee on Health Statistics noted in its 6th Report that morbidity could be measured in terms of 3 units (a) persons who were ill (b) the illnesses (periods or spells of illness) that these persons experienced; and (c) the duration (days, weeks, etc.) of these illnesses
- 25. INCIDENCE Incidence rate isdefined as the number of NEW cases occurring in a defined population during a specified period of time . It is given by the formula : Number of new cases of specific disease during a given time period Incidence = X 1000 Population at risk during that period For example:- if there had been 500 new cases of an illness in a population of 30,000 in a year, the incidence rate would be: = 500/30,000 x 1000 = 16.7 per 1000 per year
- 26. PREVALENCE The term "diseaseprevalence" refers specifically to all current cases (old and new) existing at a given point in time, or over a period of time in a given population. (a) Point prevalence (b) Period prevalence (a) Point prevalence •Point prevalence of a disease is defined as the number of all current cases (old and new) of a disease at one point of time, in relation to a defined population. several days, or even a few weeks.
- 27. Point prevalence isgiven by the formula: Number of all current cases (old and new) of a specified disease existing at a given point in time X 100 Estimated population at the same point in time Conti..
- 28. (b) Period prevalence Aless commonly used measure of prevalence is period prevalence. It measures the frequency of all current cases (old and new) existing during a defined period of time (e.g., annual prevalence) expressed in relation to a defined population. cases arising during the year. Period prevalence is given by the formula: Number of existing cases (old and new) of a specified disease during a given period of time interval X 100 Estimated mid interval population at risk Conti..
- 29. METHODS OF EPIDEMIOLOGICAL STUDIES Epidemiologistsemploy three different methods or approaches for epidemiological studies which are: 1. Descriptive method 2. Analytical method. 3. Experimental method
- 30. 1. Descriptive Method Descriptivemethod of epidemiological study is concerned with the study of frequency and distribution of disease and health related events in population in terms of person, place and time. This method gives information about which all are affected by a particular disease or health related event or problems, where the cases occur and when they occur. The data is collected about:
- 31. • Personal characteristicssuch as age, sex, race, marital status, occupation, education, income, Class, dietary pattern, habits. • Place distribution of cases i.e. areas of high concentration, low concentration and spotting in the map. • Time distribution/trends such as year, season, month, week, day and hour of onset of the disease. Conti..
- 32. Such information’s giveclue to possible associated factors such as age with specific disease e.g. measles, diphtheria, pertusis in early childhood, cancer in middle age, arterioscleroses in old age, some habits like smoking with lung cancer, dietary pattern with obesity. The data collected are analyzed and presented in terms of percentages, rates and ratios. Conti..
- 33. - Cross-sectional studies Inthis design of descriptive method of study, the data is collected from a cross-section of population at a one point in time. The results of the study are applied on the population. The cross-section of the population is sampled carefully so that it is representative of the whole population. Cross-section study is like a snapshot and provides information about the prevalence of a disease. It is also called as prevalence study. example study of diabetes or hypertension by personal characteristics and life style
- 34. - Longitudinal Studies Longitudinalstudies art useful for studying the natural history of diseases, finding out incidence rates of diseases and identifying risk factors of diseases. Longitudinal studies are more expensive and time consuming than cross- sectional studies.
- 35. 2. Analytical Method Youhave learn that descriptive studies generate etiological clues for various diseases help in formulating a guess or hypothesis for further vigorous study or testing e.g. "Cigarette smoking (10 to 20 in a day) causes lung cancer in 10 to 15% of smokers after 20 years of exposure”, wife battering is related to violence in victim's childhood family of origin". These types of hypothesis are further studied and tested by analytical studies to determine the association of cause with the effect.
- 36. - Case controlstudy In this method a group of people who have been diagnosed as having a particular problem e.g. lung cancer (cases) are compared with a group of people who are similar in characteristics to that of cases but they are free from the problem i.e. free from lung cancer under study (controls).
- 37. - Cohort Study Acohort is a specific group of people, at a certain time, sharing common characteristics or experience e.g. people born on the same day or the same year (birth cohort), couple married in the same year (marriage cohort), a class of nursing students (experience cohort), people With same occupation (occupation cohort) etc.
- 38. a) Prospective cohortstudy: Cohort study is prospective in nature because the group under study is free from the disease but exposed to risk factor and epidemiologist study the development of a condition over time. example-lung cancer b) Retrospective cohort study: This is also called as historical cohort study. In this type of study designs the event has already occurred Conti..
- 39. Experimental Method • Experimentalstudies are similar in approach to cohort studies except that conditions are under the careful control of investigator. • Experimental studies are done to confirm the etiology of diseases,' establish the efficacy of preventive or therapeutic measures and evaluate health care services. • These' studies are done under controlled conditions. • The investigator administers an intervention/gives treatment to the experimental group which is either exposure to causative factor of disease or preventive/therapeutic measure to improve or influence health or prevent disease but not to the control group which is similar to experimental group in all its aspects.