A) Introduction Epidemiology derived from word epidemic Epi = Among Demos = People Logos = Study Definition Given by John M. Last in 1988 " 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 The diseases included are Endemic diseases Epidemic diseases Chronic diseases Accidents Recently included Mental health Also included is Study of health services used by population Measurement of impact (of health services) Epidemiology is more concerned with well being of society as whole (than with well being of individuals) B) Common Components of Epidemiology Disease frequency Distribution of disease Determinants of disease 1) Disease Frequency Epidemiology is Measurement of frequency of disease, disability or death & Summarising this information in ratios and rates. Which are essential for comparing disease frequency in different populations (or subgroups of same population) in relation to suspected causal factors Such comparisons may yield important clues to disease aetiology which is vital step in development of strategies for prevention or control of health problems. Epidemiology is also Measurement of health related events and states in community (health needs, demands, tasks, etc) and variables like blood pressure, serum cholesterol , height, weight, etc 2) Distribution of Disease Study of distribution patterns of disease in a community In the various subgroups of population by time, place and person And if these patterns lead to hypotheses about causative or risk factors And if patterns can suggest or lead to measure to control or prevent the disease. Important outcome of this study is formulation of Etiological Hypothesis. This aspect of epidemiology is known as "descriptive epidemiology". 3) Determinants of Disease Feature of epidemiology is to test etiological hypothesis and identify underlying causes/risk factors of disease Which requires use of epidemiological principals and methods. This aspect of epidemiology is known as "Analytical Epidemiology". Analytical strategies help in developing scientifically sound health programmes, interventions & policies. C) Aims of Epidemiology According to International Epidemiological Association (IEA), there are 3 main aims To describe the distribution and magnitude of health and disease problems in human populations To identify etiological factors (risk factors) in the pathogenesis of disease 3.To provide the data essential to the planning, implementation and evaluation of services for the prevention control and treatment of disease setting up of priorities among these services. The ultimate aim of epidemiology is to lead to effective action : To eliminate or reduce the health problems or its consequences To promote the health and well-being of society as a whole.
D) Uses of Epidemiology Epidemiology has been defined as a "means of learning, or asking questions and getting answers that lead to further questions". In this context, Morris identified seven distinct uses of epidemiology. I ) To study historically the rise & fall of diseases in the population. It is study of history of disease in human population. Health and Disease Pattern in community is never constant, There are Fluctuations over short and long periods of time. First contribution of epidemiology to study of Coronary Heart Disease is labelling CAD as "epidemic". Epidemiology provides means to study disease profiles & time trends in human population. By study of these trends we can make useful projections into the future & identify emerging health problems and their correlates. II ) Completing the natural history of disease. Epidemiology is concerned with entire spectrum of disease in population. Epidemiologist can broadest perspective of disease as he is concerned with all cases in defined population, regardless of severity or source of medical care. Epidemiologist studies disease pattern in community in relation to agent, host and environment factors & Can better fill in gaps in natural history of disease. Contribution of epidemiology to study of Atherosclerosis is that 1/3 to 1/2 deaths occur suddenly (in one hour) which would not have shown on hospital studies as patients don't reach hospitals in time. This gave tremendous impetus to development of intensive coronary care units. Epidemiological investigations have given large amount of data on risk factors in relation to chronic diseases. III ) Community Diagnosis Epidemiology is "diagnostic tool" of community medicine. Community Diagnosis includes population distributions and profiles of illness & understanding of social, cultural and environmental characteristics of community. IV ) Planning & Evaluation Planning is essential for rational allocation of limited resources. Application of epidemiological principles to problems of heath care is "new epidemiology". Example : Planning facilities for medical care ( no. of hospital beds for specific diseases patients, health manpower planning) preventive services (Immunisation campaigns, provision of sanitary services Planning for research Evaluation : Any measures taken to control or prevent a disease must be followed by an evaluation to find out whether the measures undertaken are effective in reducing the frequency of the disease. Value of method in relation to others is assessed by cost effectiveness studies. Development of randomised controlled trial has made it possible to evaluate treatment modalities on firm scientific basis. It is not enough to know that a programme provides some benefit ; We need to know how much benefit and at what risk and cost. V ) Evaluation of Individual's Risks & Chances Epidemiologists calculate measures of Absolute Risk : Incidence Rate Specific Rates Relative Risk and Attributable Risk for a factor related to or believed to be cause of disease. Example : Risk of bearing a Mongol child and of some hereditary diseases. Risk assessment for smokers and non smokers for selected causes of disease. VI ) Searching for Causes & Risk Factors Epidemiology tries to identify cause of disease by Relating disease to Inter population differences and other attributes of population or cohorts examined Examples : Identification of Rubella as cause of congenital defects Thalidomide as teratogenic agents Cigarette smoking as cause of lung cancer In case of chronic diseases, concept of "Risk Factors" gave renewed impetus to epidemiological research. VII ) Syndrome Identification Epidemiological investigations can be used to define and refine medical syndromes That are identified by observing frequently associated findings in individual patients. Example : Differentiation of gastric and duodenal ulcer was through "poverty" gradient in gastric ulcer = Present duodenal ulcer = Absent