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Introduction to Epidemiology.pptx [Repaired].pptx

  2. 2. Introduction to Epidemiology  Definition  Basic features of Epidemiology  Branches of epidemiology  History of Epidemiology  Scope of epidemiology  Use/purpose/applications/ of Epidemiology  Basic assumptions of epidemiology  Theories disease causation  Natural history of disease  Levels of disease occurrence & level of 2
  3. 3. Introduction: Definition  The term ‘epidemiology’ comes from the Greek words epi(upon), demos(people) and logos(the study of). i.e. Epidemiology is the study of what is ‘upon the people’  Epidemiology is classically defined as: ‘the study of the distribution, determinants, and frequency of diseases & health-related problems in human populations’ and the application of this study to the prevention of disease and promotion of health 3
  4. 4. Definition… Key terms  Distribution: Epidemiology is concerned with the frequency and pattern of health events in a population.  Frequency: involves quantification of occurrence of disease or other health related problems  Pattern: occurrence of disease or health-related events by time, place, and person  Time patterns (annual, seasonal, weekly, etc)  Place patterns (geographic variation, urban/rural differences, location of work sites, etc)  Personal characteristics (demographic factors such as age, sex, marital status, and socioeconomic status) 4
  5. 5. Definition…  Determinants: factors that influence or determine the occurrence of disease & other health-related events  any definable entity that brings about change in health and health related conditions  It refers to “why diseases occur in certain places, in a certain period, Or in a certain population groups”  What makes some people healthy and others unhealthy?  The range of personal, social, economic, and environmental factors that influence health status 5
  6. 6. Definition…  Health-related states or events:-anything that affects the well-being of a population, including malnutrition, injuries, etc  Study:  Epidemiology is a scientific discipline with sound methods of scientific inquiry at its foundation.  Epidemiology is data-driven and relies on a systematic and unbiased approach to the collection, analysis, and interpretation of data. 6
  7. 7. Definition…  Application: involves applying the knowledge gained by the studies to community-based practice  The ultimate purpose of all epidemiological studies is the prevention and control of health problems 7
  8. 8. Definition…  Risk factor: an individual attribute (intrinsic characteristic of the individual) or exposure (external environmental situation) that is associated with (increases the likelihood of) the occurrence of a disease  Necessary cause: factor necessary for a disease to occur and in its absence that specific disease can’t occur. 8
  9. 9. 9 Basic features of Epidemiology 1. Studies are conducted on human population 2. It examines patterns of events in people 3. Can establish cause-effect relationship without the knowledge of biological mechanism 4. It covers a wide range of conditions 5. It is an advancing science Agumas F.
  10. 10. Types of Epidemiology Two major categories of Epidemiology 1. Descriptive Epidemiology Defines distribution (frequency and patterns) of diseases and other health related events Answers the four major questions: how many, who, where, and when? Agumas F. 10
  11. 11. Types… 2. Analytic Epidemiology Analyses determinants of health problems Answers two other major questions: how? and why? Generally, Epidemiology answers six major questions: how many, who, where, when, how and why? Agumas F. 11
  12. 12. Question 1  What are personal, social, economic, and environmental determinants of disease? 12
  13. 13. History of Epidemiology Seven land marks in the history of Epidemiology 1. Hippocrates (460BC): Environment & human behaviors affects health 2. John Graunt (1662): Quantified births, deaths and diseases 3. Lind (1747): Scurvy could be treated with fresh fruit 4. William Farr (1839): Established application of vital statistics for the evaluation of health problems Agumas F. 13
  14. 14. History… 5. John Snow (1854): tested a hypothesis on the origin of epidemic of cholera 6. Alexander Louis (1872): Systematized application of numerical thinking (quantitative reasoning) 7. Bradford Hill (1937): Suggested criteria for establishing causation Epidemiological thought emerged in 460 BC Epidemiology flourished as a discipline in 1940s Agumas F. 14
  15. 15. Scope of Epidemiology Originally, Epidemiology was concerned with investigation & management of epidemics of communicable diseases Lately, Epidemiology was extended to endemic communicable diseases and non- communicable infectious diseases Recently, Epidemiology can be applied to all diseases and other health related events Agumas F. 15
  16. 16. Scope of epidemiology  In general Currently, Epidemiology Used in all kinds of diseases-communicable, non- communicable or injury category, in laboratory sciences, clinical medicine and public health  Ranges from routine surveillance to research strategies for the testing of hypotheses 16
  17. 17. Purposes of epidemiology The ultimate purpose of Epidemiology is prevention of diseases and promotion of health How?  Establish causation of disease  Elucidate the natural history of disease  Describe the health status of the population  Identify determinants of diseases  Evaluation of intervention programs  Classification of diseases 17
  18. 18. Purposes… 1. Establish causation of disease  Causation-is an antecedent factor that was necessary for the occurrence of the disease at the moment it occurred 2. Studies the natural history of diseases  is essential to make (study) prognosis or the likely outcome of a patients illness  Gives basis for rational decision about therapy 18
  19. 19. Purposes… 3. Description of health status of populations:  Measure disease frequency- quantify disease  Assess distribution of disease  Who is getting disease?  Where is disease occurring?  When is disease occurring?  Formulation of hypotheses concerning causal  and preventive factors 19
  20. 20. Purposes… 4. Identify determinants of diseases:  Hypothesis is developed after description of occurrence by person, place and time.  Hypotheses are tested using epidemiologic studies  =>Determinants:  lifestyle, poverty, health care facilities, environment  If we can identify determinants of disease, lead or helps to prevention and control of 20
  21. 21. Purposes… 5. Evaluation of intervention programs:  assessing whether the measures (programs designed to prevent and control a disease) are effective in reducing the frequency of the d/se or not 6. Classification of diseases:  e.g. based on route of transmission 21
  22. 22. Purposes…  Is epidemiology of importance to environmental health professionals?  In what aspects? 22
  23. 23. Basic Epidemiologic Assumptions Two fundamental assumptions:  Human disease does not occur at random:  some behavioral and environmental factors (exposures) increase the risk of acquiring/developing a particular disease among group of individuals  Human disease has causal and preventive factors  identified through systematic investigation of populations, creating opportunity for prevention and control the diseases, either by eliminating the cause or introducing appropriate treatment 23
  24. 24. Concepts of Disease Occurrence (causation)  A critical premise of epidemiology is that diseases do not occur randomly in a population,  are more likely to occur in some members of the population than others b/se of risk factors that may not be distributed randomly  Causation  A number of models of disease causation have been proposed,  The simplest of these is the epidemiologic triad or triangle, the traditional model for infectious disease 24
  25. 25. Concepts of Disease Occurrence…  Epidemiologic triad is a model of disease causation famous in epidemiology  The triad consists of an external agent, a susceptible host, and an environment that brings the host and agent together  In this model, disease results from the interaction b/n the agent and the susceptible host in an environment that supports transmission of the agent from a source to that host 25
  26. 26. Concepts of Disease Occurrence…  Agent, host, and environmental factors interrelate in a variety of complex ways to produce disease  Development of public health measures to control or prevent disease usually requires assessment of all three components and their interactions 26
  27. 27. Concepts of Disease Occurrence…  Figure :1 Epidemiologic Triad 27
  28. 28. Concepts of Disease Occurrence… Agent  originally referred to an infectious microorganism or pathogen: a virus, bacterium, parasite, or other microbe  Generally, the agent must be present for disease to occur; however, presence of that agent alone is not always sufficient to cause disease  A variety of factors influence whether exposure to an organism will result in disease, including the organism's pathogen city (ability to cause 28
  29. 29. Concepts of Disease Occurrence…  Over time, the concept of agent has been broadened to include chemical and physical causes of disease or injury  While the epidemiologic triad serves as a useful model for many diseases, it has proven inadequate for cardiovascular disease, cancer, and other diseases that appear to have multiple contributing causes without a single necessary one. 29
  30. 30. Concepts of Disease Occurrence… Host  Refers to the human who can get the disease  A variety of factors intrinsic to the host, sometimes called risk factors, can influence an individual's exposure, susceptibility, or response to a causative agent  Opportunities for exposure are often influenced by behaviors such as sexual practices, hygiene, and other personal choices as well as by age and sex. 30
  31. 31. Concepts of Disease Occurrence… Environment  Refers to extrinsic factors that affect the agent and the opportunity for exposure  Environmental factors include:  physical factors such as geology and climate,  biologic factors such as insects that transmit the agent, and  socioeconomic factors such as crowding, sanitation, and the availability of health services 31
  32. 32. Examples of causes of disease by host, agent and environmental factors. Host factors Agent factors Environmental factors Age  Sex  Previous disability  Behaviors  Genetic inheritance  Height  Weight Virulence of organisms  Serotype of organisms  Antibiotic resistance Cigarette-tar content Home overcrowding  Air pollution  Workplace Hygiene  Weather  Water composition  Food contamination  Animal contact 1/26/2023 By: Agumas F.
  33. 33. Reading Assignment 1. What does mean causation? 2. Necessary vs. sufficient cause 3. Theories of disease causation? 4. How do diseases develop (Disease causation models (concepts))? 4.1. Epidemiologic triad 4.2. Web causation?? 4.3. wheel causation?? 33
  34. 34. 34 Agumas F.
  35. 35. 35 1/26/2023 Agumas F
  36. 36. COURSE TITLE: Natural History of Disease and Level of Disease Prevention BY: Agumas Fentahun (BSC in HO, MPH in Epidemiology) 36
  37. 37. Natural History of Disease and Level of Disease Prevention 37
  38. 38. Natural history of disease • refers to the progression of disease process in an individual over time, in the absence of intervention • It is the course of illness in the absence of intervention • begins with exposure to the causative agent • ends with recovery, disability, or death • Has four stages – Stage of susceptibility – Stage of pre-symptomatic (sub-clinical) disease – Stage of clinical disease – Stage of disability or death 38
  39. 39. Natural history of disease… 1. Stage of susceptibility • In w/c, disease has not yet developed, but the groundwork has been laid by the presence of factors that favor its occurrence – Example: unvaccinated child is susceptible to measles 2. Stage of Pre-symptomatic (sub-clinical) disease • no manifestations of the disease but pathologic changes have started to occur in the body • detected through special tests • may lead to the clinical stage, or ends in recovery 39
  40. 40. Natural history of disease… • Examples: – Detection of antibodies against HIV in an apparently healthy person – Ova of intestinal parasite in the stool of apparently healthy children 40
  41. 41. Natural history of disease… 3. The Clinical stage • Characterized by signs and symptoms of the disease • varies in duration, severity and outcome for d/t diseases • May end with recovery, disability or death 41
  42. 42. Natural history of disease… Examples: • Common cold: has a short and mild clinical stage and almost everyone recovers quickly • Polio: has a severe clinical stage and many patients develop paralysis • Rabies: has a relatively short but severe clinical stage and almost always results in death • Diabetes Mellitus: has a relatively longer clinical stage and eventually results in death if the patient is not properly treated 42
  43. 43. Natural history of disease… 4. Stage of disability, death or recovery where the out come of the disease observed • Disability is a physical or mental condition that limits a person's movements, senses, or activities. • Examples: – Trachoma may cause blindness – Meningitis may result in blindness or deafness, or death 43
  44. 44. Fig1: Natural History of Disease Timeline 44 Natural history of disease…
  45. 45. Level of disease occurrences Level of disease • Endemic: a persistently low to moderate level of occurrence of disease • Epidemic: presence of disease in excess of the usual occurrence • Outbreak: carries the same definition of epidemic, but is often used for a more limited geographic area. It is an epidemic restricted by place, person and time 45
  46. 46. Level of disease… • Pandemic-an epidemic that has spread over several countries or continents • Hyper-endemic: a persistently high level of occurrence of a disease • Sporadic: refers to a disease that occurs infrequently and irregularly. • Cluster: refers to an aggregation of cases grouped in place and time that are suspected to be greater than the number expected, even though the expected number may not be known. 46
  47. 47. Level of disease… An epidemic may result from: – A recent increase in amount or virulence of the agent – The recent introduction of the agent into a setting where it has not been before, – An enhanced mode of transmission so that more susceptible persons are exposed, – A change in the susceptibility of the host response to the agent, and/or – Factors that increase host exposure or involve introduction through new portals of entry 47
  48. 48. Levels of Disease Prevention • The major purpose in investigating the epidemiology of diseases is to learn how to prevent and control them • Disease prevention means to interrupt or slow the progression of disease 48
  49. 49. Levels of Disease prevention Primordial prevention Primary prevention Secondary prevention Tertiary prevention 1/26/2023 By: Agumas F.
  50. 50. Eradication and Elimination Eradication: • It is termination of all transmission of infection by extinction of the infectious agent through surveillance. it is an absolute process, an “all or none” phenomenon, restricted to termination of infection from the whole world. Elimination: • Is sometimes used to describe eradication of a disease from a large geographic region. • Disease which are amenable to elimination in the meantime are polio, measles and diphtheria. 1/26/2023 By: Agumas F.
  51. 51. Level Of disease Prevention 1. Primordial prevention • Primordial prevention consists of actions and measures that inhibit the emergence of risk factors in the form of – environmental, – economic, – social, – behavioral conditions and cultural patterns of living etc. 1/26/2023 By: Agumas F.
  52. 52. Level of Disease prevention 2. Primary prevention • Any action that are taken prior to the onset of disease, which removes the possibility that the disease will ever occur. • It signifies the intervention in the pre- pathogenesis phase of a disease. 1/26/2023 By: Agumas F.
  53. 53. Levels of Disease Prevention… 2. Primary prevention:-keeps the disease process from becoming established by eliminating causes of disease or increasing resistance to disease • Has 3 components – These are health promotion, prevention of exposure, and prevention of disease 53
  54. 54. Levels of Disease Prevention… 2.1. Health promotion:- consists of general non- specific interventions that enhance health and the body's ability to resist disease – Improvement of socioeconomic status, provision of adequate food, housing, clothing, and education are examples of health promotion 2.2. Prevention of exposure:- is the avoidance of factors which may cause disease if an individual is exposed to them – Examples can be provision of safe and adequate water, proper excreta disposal, and vector control. 54
  55. 55. Levels of Disease Prevention… 2.3. Prevention of disease:- is the prevention of disease development after the individual has become exposed to the disease causing factors – Immunization is an example of prevention of disease – it acts after exposure has taken place – It does not prevent an infectious organism from invading the immunized host, but does prevent it from establishing an infection – eg. measles vaccine, will not prevent the virus from entering to the body but it prevents the development of infection/disease 55
  56. 56. Levels of Disease Prevention… 3. Secondary prevention:-is to stop or slow the progression of disease so as to prevent or limit permanent damage – can be achieved through detecting people who already have the disease as early as possible and treat them – It is carried out before the person is permanently damaged • Eg diagnosing and treatment of a certain individual 56
  57. 57. Levels of Disease Prevention… Examples: • Prevention of blindness from Trachoma • Early detection and treatment of breast Ca to prevent its progression to the invasive stage 57
  58. 58. Level of Disease prevention 4. Tertiary prevention: Is targeted towards people with permanent damage or disability If primary and secondary preventions have failed, and When primary and secondary prevention are not effective 58
  59. 59. Levels of Disease Prevention… • It has two objectives: 1. Treatment to prevent further disability or death and 2. To limit the physical, psychological, social, and financial impact of disability-improving the quality of life This can be done through rehabilitation, which is the retraining of the remaining functions for maximal effectiveness Example: in blindness due to vitamin A deficiency, tertiary prevention (rehabilitation) can help the blind or partly blind person learn to do gainful work and be economically self supporting 59
  60. 60. Thank you! 1/26/2023 Getasew M. 60

Editor's Notes

  • Antecedent = precursor
  • Premise = bases = principle = ground