CHAPTER 4.pptx
- 1. CHAPTER 4 EPIDEMIOLOGY Qassim Awale MPH,HN&D
- 2. DEFINITION • Epi- among, upon; • Demos = people, population; • Logos = science, study.
- 3. DEFINITION • Epidemiology has been defined as, ‘The study of distribution and determinants of health related states or events in specified populations and application of this study to the control of health problems’ (John M Last, 1988).
- 4. EVENTS • The health related events are all the conditions of the spectrum of health such as disease, injury, disability and death. • These events are with reference to the human population.
- 5. DISTRIBUTION • This refers to the pattern of occurrence of disease in the community with reference to time, place and person. • This helps to study the trend of the disease over the years (decades), geographical areas and over different population groups.
- 6. CONTINUE • This study also helps to know the magnitude of the problem, gives a clue about the etiology, mode of transmission of the disease.
- 7. DETERMINANTS • This refers to the etiological or risk factors related to particular disease. This study helps to test the etiological hypothesis formulated. • This aspect of epidemiology dealing with testing the hypothesis is known as ‘Analytical epidemiology.
- 8. DISEASE FREQUENCY • This means measuring the magnitude or extent of the health related event or health problem in the community, in terms of morbidity rates such as incidence and prevalence and also in mortality rates. These are expressed in terms of rate, ratio and proportion. This helps to compare with that of other countries or other groups of population in the same country (Morbidity means sickness and Mortality means deaths).
- 9. OBJECTIVES OF EPIDEMIOLOGY • To know the distribution of the disease in the community. • To know the magnitude of the problem • To identify the etiological and risk factors in the development of disease
- 10. CONTINUE • To plan for the implementation of prevention and control measures • To eliminate or eradicate the disease • To evaluate the control measures • Ultimate objective is to promote the health and wellbeing of the people.
- 11. EPIDEMIOLOGICAL APPROACH • It is an approach to achieve the above objectives by collecting the data by asking the following questions and analyzing the data systematically: • What is the event? (Nature of the disease) • When did the disease occur? (Time distribution of the disease) • Where did the disease occur? (Place distribution of the disease) • Who are the persons affected? (Person distribution of the disease) • What is the extent of the problem? (Magnitude) • Why did it occur? (Etiology) • What is to be done to reduce the problem? (Control measures) • How can it be prevented in future? (Preventive measures)
- 12. Measurements in Epidemiology • The magnitude of the health problem in the community is measured in terms of diseases (morbidity) and deaths (mortality). • It is expressed in terms of rates, ratios and proportions, which are called ‘Basic tools’ in epidemiology.
- 13. Rate • It measures the occurrence of an event (disease or death) in a given population, during a given period of time, usually one year, e.g. death rate, birth rate, growth rate, accident rate, etc. • Death rate is the rate at which the people are dying in a given area, during a given period of time.
- 14. Continue • for example, out of 500 juveniles in a juvenile home, while 200 are found to be delinquents.
- 15. RATIO • This expresses a relation between the two quantities. The numerator is not a component of the denominator. It is expressed as x/y or x: y. • In the above example, the juvenile delinquency ratio is 200: 300, i.e. 2 : 3.
- 16. MEASUREMENT OF MORBIDITY • This means determining the quantum of disease in the community (i.e. disease load). • When the survey is carried out over a period of time (minimum one year) it is called longitudinal survey or incidence survey, which helps to find out the occurrence of NEW cases, of a specified disease. • When the survey is carried out at a given point of time or a particular period, it is called cross sectional or horizontal or prevalence survey, which helps to find out the existence of both OLD and NEW cases in total, of a specified disease. • Thus, morbidity is measured and expressed in two ways— incidence and prevalence rates. • (Incidence is obtained from longitudinal studies and prevalence from cross-sectional studies).
- 17. INCIDENCES • Incidence rate number of new cases of a specified disease in a given area during a given period of time. • It is the occurrence of only NEW (fresh) cases of a specified disease in a given area, during a given period of time (minimum one year).
- 18. PREVALENCE • It refers to the existence of all cases (both old and new) of a specified disease at a given point (point prevalence) or a given period of time (period prevalence), in a given population. • The point of time may be hour, day or week. The period of time may be months or years. Period prevalence is the sum of point prevalence, at the beginning of the specified period and the incidence during that period
- 19. Differences B/W Prevalence & Incidence Incidence Prevalence Refers to occurrence of new cases only in a given area, during a given year. Refers to existence of both old and new cases in a given area, during a given period/point of time. Refers to acute cases having short incubation period. Prevalence rate is useful to know the magnitude of the problem Not influenced by duration of illness. Prevalence is not an ideal measure to study the etiology of a disease. Incidence rate is an ideal measure to study the etiology of a disease Refers to chronic cases having long incubation period Incidence rate helps to evaluate the control measures Prevalence rate helps for health planning. Examples, measles Ex: Tuberculosis, leprosy, etc
- 20. EPIDEMIOLOGICAL STUDIES (METHODS) • There are two types epidemiological studies 1. Observational. 2. Experimental. • OBSERVATIONAL STUDIES: are based on the field observations made on the experiments carried out by nature. They are of two types namely A. descriptive B. analytical studies.
- 21. A. Descriptive Studies (Descriptive Epidemiology) • These are concerned with observation of the distribution of a disease in a community, with reference to time, place and person, and identifying the associated characteristics of the disease to formulate an etiological hypothesis.
- 22. PROCEDURES • Defining the population of the community • Defining the disease under study • Describing the distribution disease with reference to time, place and person • Measurement of disease • Formulation of etiological hypothesis.
- 23. TIME DISTRIBUTION • This means describing the time of occurrence/onset of the disease with reference to year, month, week, day, hour of onset, season, atmospheric temperature, climate etc. This study often gives a clue about the etiology of the disease or the predisposing factors, so that preventive measures can be adopted.
- 24. PLACE DISTRIBUTION • This means the pattern of occurrence of a disease in different places. • This helps to compare the disease occurrence from one country to another country, and within the same country from one state to another state, from rural to urban areas and local areas.
- 25. PERSON DISTRIBUTION • This means describing the distribution of a disease in the community with reference to the host characters of the persons affected, such as age, sex, occupation, literacy level, marital status, social class, behavior, and such other factors.
- 26. B. ANALYTICAL STUDIES (ANALYTICAL EPIDEMIOLOGY) • This is also an observational study of epidemiology which deals with testing the etiological hypothesis, formulated.
- 27. Uses of Descriptive Epidemiology • It helps to know the extent/magnitude of the disease in the community, in terms of morbidity and mortality rates. • It helps to know the distribution of the disease with reference to time, place and person. • It helps to identify the risk group. • It helps to formulate an etiological hypothesis. • It helps to plan, organize and implement curative and preventive services. • It helps in doing research.
- 28. Experimental Epidemiology (Experimental Epidemiological Studies) • Experimental studies are also called ‘Intervention studies’. In this study, some action or intervention is involved such as deliberate application (of a drug) or withdrawal of the suspected cause in the experimental (or study) group and no change in the control group. • Later the outcome of the experiment is compared in both the groups.
- 29. CONTINUE • it differs from the observational studies in that the experiment is directly under the control of the investigator and involves cost, ethics and feasibility whereas in the observational studies the investigator (epidemiologist) takes no action but only observes the outcome.
- 30. USES OF EPIDEMIOLOGY • 1. It helps to study the natural history of a disease, i.e. in relation to agent, host and environmental factors and further evolution of the disease to its termination as death or recovery, in the absence of prevention or treatment. This is a necessary framework for application of preventive measures.
- 31. CONTINUE • 2. It helps to measure the disease frequency in terms of the magnitude of the problem (i.e. morbidity and mortality rates). • 3. It helps to make ‘Community diagnosis’ by studying the distribution of the disease with reference to time, place and person.
- 32. CONTINUE • 4. It helps to make researches in epidemiology. • 5. It helps to identify the determinants of the disease and the risk factors. 6. It helps to ‘evaluate’ the health services to find out whether the measures undertaken are effective in controlling the disease or not. Further it also helps to find out the cost- effectiveness of different methods.
- 33. SL N O EPIDEMIOLOGY CLINICAL MEDICINE 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.
- 36. •THE END