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Epidemiology

This article provides an overview of epidemiology, the study of the distribution and determinants of health-related states in populations. It covers the objectives, purposes, and components of epidemiology, including disease frequency, distribution, determinants, and methods of investigation.

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Epidemiology

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  1. Epidemiology

  2. Classically speaking • Epi = upon (among) • Demos = people • Ology = science • Epidemiology = the science which deals with what falls upon people…..

  3. A Modern Definition • “The study of the distribution and determinants of health-related states in specified populations, and the application of this study to control health problems." (Last J) Search for knowledge Apply in health service

  4. Objectives of Epidemiology 1. To describe the distribution and magnitude of health and disease problems in the population. 2. To identify the etiological factors – risk factors in the population. 3. To provide the data essential to planning, implementation and evaluation of services for prevention, control and treatment of disease and to setting up of priorities for these services.

  5. The ultimate aim of epidemiology is • to eliminate or reduce health problem or its consequences and • to promote health and well-being of society as a whole.

  6. Purposes of Epidemiology To investigate nature / extent of health-related phenomena in the community / identify priorities To study natural history and prognosis of health-related problems To identify causes and risk factors To recommend / assist in application of / evaluate best interventions (preventive and therapeutic measures) To provide foundation for public policy

  7. Component: Disease Frequency- Rate and Ratio e.g Rate- incidence rate, prevalence rate etc Ratio- sex ratio, doctor-population ratio Distribution of Disease- Disease in community find causative factor Generate hypothesis Descriptive epidimiology

  8. Determinants of Disease- To test hypothesis Analytic epidemiology Help in develop sound scientific program

  9. Incidence • Number of new cases of a disease which come into being during a specified period of time. (Number of new cases of specific disease during a given period)/(population at risk during that period) x 1000 Importance: If incidence increasing, it may indicate failure or ineffectiveness of control measure of a disease and need for better/new health control measure.

  10. Prevalence • Number of current case (old and new) of a specified disease at a point of time • It help to estimate the burden of disease • Identify potentially high-risk populations. They are essentially helpful to plan rehabilitation facilities, manpower needs, etc. (Number of current case of a specified disease at a point of time)/(estimated population at the same point of time) x 100 • Point prevalence AND Period prevalence

  11. Relationship between incidence and prevalence • Prevalence =Incidence x Duration

  12. Approach of an epidemiologist • Asking questions • making comparisons ● Asking questions may provide clues to cause or aetiology of disease e.g. What is the event, what is its magnitude, where did it happen, when did it happen, who were affected, why did it happen?

  13. Making comparisons will help draw inferences to support asking questions. • This comparison may be: ● Between those with the disease and those without the disease; ● Those with risk factor and those not exposed to risk factor;

  14. Terms to know • Endemic: constant presence of a disease in a given population • epidemic: outbreak or occurrence of one specific disease from a single source, in a group population, community, or geographical area, in excess of the usual level of expectancy • pandemic: epidemic that is widespread across a country, or large population, possible worldwide

  15. Three essential characteristics that are examined to study the cause(s) for disease in analytic epidemiology are... • Host • Agent • Environment

  16. Host Factors • Behaviors • Genetic predisposition • Immunologic factors • Influence the chance for disease or its severity

  17. Agents • Biological • Physical • Chemical • Necessary for disease to occur

  18. Environment • External conditions • Contribute to the disease process

  19. Epidemics arise when host, agent, and environmental factors are not in balance • Due to new agent • Due to change in existing agent (infectivity, pathogenicity, virulence) • Due to change in number of susceptibles in the population • Due to environmental changes that affect transmission of the agent or growth of the agent

  20. EPIDEMIOLOGICAL METHODS . The methods he employs can be classified as: 1. Observational studies a. Descriptive studies b. Analytical studies – Case control studies – Cohort studies 2. Experimental/interventional studies – Randomized control studies – Field trials – Community trials

  21. Descriptive Studies Steps in conducting a descriptive study. Descriptive studies form the first step in any process of investigation. These studies are concerned with observing the distribution of disease in populations. 1. Defining the population. 2. Defining disease under study. 3. Describing the disease. 4. Measurement of disease 5. Compare 6. Formulate hypothesis-

  22. Defining the population. Defined population may be the whole population or a representative sample. • It can also be specially selected group such as age and sex groups, occupational groups, hospital patients, school children, small community, etc.

  23. 2. Defining disease under study. 3. Describing the disease. Disease is examined by the epidemiologist by asking three questions: ● When is the disease occurring—time distribution? ● Where is it occurring—place distribution? ● Who is getting the disease—person distribution?

  24. A. Time Distribution • Short-term fluctuations. Epidemic Common source epidemics - single exposure/point source—bhopal tragedy Propagated-infectious - • Periodic fluctuations; Seasonal –measles (early spring) cyclic- ,, in pre-vaccinated era (peak 2-3 yr) • Long-term or secular trends; diabetes, CVD

  25. B. Place Distribution • International variations: Cancer of stomach very common in Japan less common in US. oral cancer- India Breast cancer- Low-japan, high-western • National variations, e.g. Distribution of fluorosis,

  26. Rural-urban differences, e.g. CVD, Mental illness more common in urban areas. Skin diseases, worm infestations more common in rural areas. • Local distributions, e.g. Spot maps- John Snow in London to incriminate water supply as cause of cholera transmission in London.

  27. cholera cases in proximity to water pump, 1854

  28. C. Person Distribution Age:e.g. Measles is common in children, Cancer in middle age Degenerative diseases in old age. Sex: Women- Lung cancer-less Hyperthyroidism- more c. Social class- Diabetes, Hypertenson– upper class

  29. 4. Measurement of disease- Mortality/ Morbidity 5. Compare- Between different population, subgroups 6. Formulate hypothesis. On basis of all data epidemiologist form hypothesis.

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