EPIDEMIOLOGY

EPIDEMIOLOGY

1. EPIDEMIOLOGY Presented By Flavia.Dass 1 st year M.sc. Nursing KIMS Hubli

2. INTRODUCTION The term epidemiology is derived from the Greek word epidemic. Epi meaning “ upon or among” Demos meaning “people or district” Logos meaning “scientific study” The distinction between epidemic (visited on a population) and endemic ( reside within a population) was first drawn by Hippocrates. The term ‘epidemiology’ appears to have first been used to describe the study of epidemics in 1802 by the Spanish physician Villalba.

3. DEFINITIONS The science of infective diseases , their prime causes, propagation and prevention. (Stallbrass 1931) The study of the disease, any disease, as a mass phenomenon.( Greenwood 1935) The study of the distribution and determinants of health related states or events in specified population and application of the study to control of health problems. (J.M. Last 1988)

4. HISTORY The Greek physician Hippocrates has been called the father of epidemiology. He is the first person known to have examined the relationships between the occurrence of disease and environmental influence. In the middle of the 16 th century, a doctor from Verona named Girolamo Fracastoro was the first to propose a theory that these very small, unseenable , particles that cause disease were alive. They were considered to be able to spread by air, multiply by themselves and to be destroyable by fire. John Graunt , a professional haberdasher and serious amateur scientist , presented one of the first life tables in report time trends for many diseases, new and old.

5. Dr. John Snow is famous for his investigation into the causes of the 19 th century cholera epidemics. His identification of the Broad Street pump as the cause of the Soho epidemic is considered as a classic example. Other pioneers include Danish physician Peter Anton Schleisner who is 1849 worked on prevention of epidemic neonatal tetanus Hungarian physician Ignaz Semmelweis in 1847 brought down infant mortality at a Vienna hospital by instituting a disinfection procedure. British surgeon Joseph Lister discovered antiseptics in 1865 in the light of the work of Louis Pasteur. In the early 20 th century, mathematical methods were introduced in epidemiology by Ronald Ross, Anderson Gray McKendrick and others.

6. SCOPE OF EPIDEMIOLOGY Originally , Epidemiology was concerned with investigation & management of epidemics of communicable disease. Lately , Epidemiology was extended to endemic communicable disease and non- communicable infection diseases. Recently , Epidemiology can be applied to all disease and other health related events.

7. AIMS OF EPIDEMIOLOGY According to the international Epidemiological association (IEA) epidemiology has 3 main aims. To describe the distribution and magnitude of health and disease problems in human populations. To identify etiological factors in the pathogenesis of disease. To provide the data essential to the planning, implementation and evaluation of services for the prevention, control and treatment of disease and to the setting up of priorities among those services.

8. The ultimate aim of epidemiology is to lead to effective action: To eliminate or reduce the health problem or its consequences To promote the health and well being of society as a whole.

9. EPIDEMIOLOGICAL APPROACHES The epidemiological approach to problems of health and disease is based on two major foundations. Asking questions Making comparison

10. 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? What is the magnitude? Where did it happen? Who are affected? Why did it happen?

11. Related to health action What can be done to reduce the problem and its consequences? How can it be prevented in the further? What action should be taken by the community? By the health services, By other sector? where and for whom these activities be carried out? What resource are required? How are the activities be organized? What difficulties may arise, how mighty they be overcome?

12. b. Making comparison The basic approach in epidemiology is to make comparisons and draw inferences. This may be comparison of two or more groups. One group having the disease and the other group or groups not having the disease or comparison between the individuals. By making this comparison, the epidemiologist tries to find out the crucial difference in the host and the environmental factors between those affected and not affected. In short the epidemiologist weighs, balances and contrast .

13. EPIDEMIOLOGIC METHODS The primary concern of the epidemiology is to study disease occurrence in people, who during the course of their lives are exposed to numerous factors & circumstances some of which may have a role in disease aetiology . Epidemiological studies can be classified into observational studies and experimental studies with subdivisions.

14. OBSERVATIONAL EPIDEMIOLOGY This method, begins with surveillance of population using vital and health statistics including analysis of death rates arranged by age, sex, locality and cause death. Other information is derived from registries of cancer or other diseases and from hospital discharge statistics All such source of information combine to make it possible to produce a multidimensional ‘community diagnosis’.

15. Observational studies Descriptive studies- study is limited to a description of the occurrence of a disease Analytic studies- goes further by analyzing relationship of the occurrence of a disease in a population Ecological or correlational (with population as unit of study) Cross- sectional or prevalence ( with individual as a study unit) Case – control or case reference (with individual as study unit) Cohort or follow up (with individual as a unit of study)   Experimental studies Randomized controlled trail or clinical trial ( with patients as unit of study) Field trails or community intervention studies (with healthy people as study) Community trails ( with community as a unit of study)

16. 1.DESCRIPTIVE METHOD Descriptive studies are the first phase of an epidemiological investigation. These studies are concerned with observing the distribution of disease or health characteristics with which the disease in question seems to be associated.

17. Basically as the questions When is the disease occurring? Where is it occurring? Who is getting the disease The various procedure involved in descriptive studies. Defining the population to be studied Defining the disease under study Describing the disease Measurement of disease Comparing with known indices Formulation of an etiological hypothesis

18. 1.Defining the population to be studied The first step is to define a ‘population base’ not only in terms of total number, but also its composition in terms of age, sex, occupation etc. 2. Defining the disease under study Once the population is defined or specified, the define the disease or condition being investigated. The main concern is to obtain an accurate estimate of disease in a population, needs a definition that is both precise & valid to enable him to identify those who have disease from those who don’t.

19. 3.Describing the disease The primary objective is to describe the occurrence and distribution of disease by time, place & person & identify those characteristics associated with presence or absence of disease in an individual. Time distribution Short term fluctuations Periodic fluctuations Long term secular trends

20. Types of epidemics Common source epidemics Single exposure epidemics Continues or multiple exposure epidemics Propagated epidemics Person to person Arthropod vector Animal reservoir Slow epidemics  

21. Place distribution This one of the important dimensions of epidemiology. Classification of variations International variations National variations Rural urban variations Local variations

22. Person distribution The disease is further characterized by defining the person who develop the disease by following factors Age Sex Ethnicity Marital status Occupations Social class Behavior Stress Migration

23. 4. Measuring the disease It is mandatory to have a clear picture of the amount of disease in the population. This is done by the use of Cross- sectional studies Longitudinal studies 5. comparing with known indices By making comparison, it is often possible to formulate hypothesis relating to disease aetiology . 6. Formulating of hypothesis.

24. 2. ANALYTIC OBSERVATIONAL STUDIES The possibilities of observational epidemiology are considerable, but not limitless. They are powerfully reinforced by analytic studies. The two main methods are Case control study Cohort study

25. CASE CONTROL STUDY 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 characteristic to that of cases but they are free from the problem i.e. free from lung cancer under study (controls).

26. There are 4 basic steps in conducting a case control study. Selection of cases & control Matching Measure of exposure Analysis

27. COHORT STUDY A cohort is a specific group of people, at a certain time, sharing common characteristics or experience e.g. people on the same day or same year (birth cohort), couple married in the same year (marriage cohort), a class of nursing students (experience cohort), people with same occupation (occupational cohort) etc.

28. Distinguishing features of cohort studies The are identified prior to the appearance of disease under investigation The study group, so defined, are observed over a period of time to determine the frequency of disease among disease The study proceeds forward from cause to effect. Types of cohort studies Prospective cohort study Retrospective cohort study

29. Prospective cohort study: Cohort study is prospective in nature because the group under study is free from disease but exposed to risk factor and epidemiologist study the development of a condition over time. E.g. lung cancer. Retrospective cohort study: This is also called historical cohort study. In this type of study designs the event has already occurred.

30. Elements of a cohort study Selection of study subject Obtaining data on exposure Selection of comparison group Follow up Analysis

31. 3. EXPERIMENTAL METHOD Experimental studies are similar in approach to cohort studies except that the condition are under the careful control of investigator. Experimental studies are done to confirm the etiology of diseases, establish the efficacy of preventive or therapeutic measure and evaluation health care services.

32. These studies are done under two ways Randomized controlled trails Non Randomized controlled trails 1.Randomized controlled trails Is a form of human experimentation in which the subjects, usually patients, are randomly allocated to receive either standard accepted therapeutic or preventive regimen, or an experimental regimen.

33. The basic steps includes Drawing up a protocol Selecting reference & experimental population Randomization Manipulation Follow up Assessment  

34. 2.Randomized controlled trails Although the experimental method is almost always to preferred , it is not always possible for ethical, administrative & other reasons to resort to a randomized controlled trail in human being  

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