CHAPTER 1 ITRODUCTION TO EPIDEMIOLOGICAL METHODS.pptx

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1. MEKELLE UNIVERSITY COLLEGE OF HEALTH SCIENCES SCHOOL OF PUBLIC HEALTH DEPARTMENT OF EPIDEMIOLOGY EPIDEMIOLOGY LECTURE NOTE BY DAWIT Z.

2. Chapter one INTRODUCTION TO EPIDEMIOLOGY Definition, principles, concepts, and basic assumptions in epidemiology

3. Objectives After completing this session, we will be able to: Define Epidemiology and describe its components Distinguish between analytic and descriptive Epidemiology Understand history and scope of Epidemiology Describe the basic assumptions and uses of Epidemiology

4. INTRODUCTION… Definition of epidemiology?

5. Epidemiology Epidemiology comes from the Greek roots: “Epi” = on or upon “Demos” = people or population “Logos” = study of So epidemiology is the study of what happens in a population

6. Epidemiology: Definition Epidemiology is the study of the  frequency,  distribution and  determinants of diseases and other health related states or events in specified populations and the application of this study to the promotion of health, and to the prevention and control of health problems . 8/9/2023 6

7. INTRODUCTION… Key words in the definition are : Study It is a basic science of public health It is a discipline that approaches problems systematically and quantitatively It has, at its foundation, sound methods of scientific inquiry.

8. INTRODUCTION… Frequency : Quantification of the existence/occurrence of disease It answers the question How many ? Epidemiology is a quantitative science

9. INTRODUCTION… Distribution Refers to how disease is distributed throughout the population Time (seasonal fluctuation, Long term variations ) Place (geographical distribution of disease) Lowland Vs Highland Urban Vs Rural Person Young Vs Old Female Vs Male Rich Vs Poor (when, where, and to whom does disease occur ?) Descriptive epidemiology

10. INTRODUCTION… Determinants: These are the factors which determine whether or not a person will get a disease or the causative factors for disease refers to the: ‘ why’: cause, risk factors Genetic Vs environmental Social and cultural conditions How: mechanism: Mode of transmission Analytical epidemiology

11. INTRODUCTION… Health related States / events It includes Acute and chronic diseases Events such as injuries Conditions such as disabilities Behaviors Genetic characteristics Vital events Social vactors- poverty Etc.

12. INTRODUCTION… Population Epidemiology focuses on populations rather than individuals. So the epidemiologist’s “patient” is the community

13. INTRODUCTION… Application- The ultimate purpose of all epidemiological studies is the prevention and control of health problems. So Epidemiological studies have direct and practical applications for prevention of diseases, control diseases & promotion of health Epidemiology is a science and practice Epidemiology is an applied science!

14. USES/purpose OF EPIDEMIOLOGY The ultimate purpose of Epidemiology is prevention and control of disease, in an effort to improve the health status of populations. How ?

15. Functions of epidemiology Discover the agent, host, and environmental factors - for the prevention of disease and injury, and the promotion of health. Determine the relative importance of causes of illness, disability, and death - establish priorities for research Identify population at the greatest risk from specific causes of ill health

16. Functions of epidemiology cont’d … Evaluate the effectiveness of preventive and therapeutic health programs and services in improving the health of the population Study the natural history of disease from its precursor states through its manifestations and clinical course Conduct surveillance of disease, injury and risk factors Investigate outbreaks - Identify their source and controlling epidemics

17. Functions of epidemiology cont’d … Monitoring the Health of Population Looking for causes of disease, death and disability - aetiological agents Evaluating interventions and health service provision

18. Functions of epidemiology cont’d … Planning health services Decision making in clinical medicine

19. Core Epidemiologic Functions • In the mid-1980s, five major tasks of epidemiology in public health practice were identified: Public health surveillance, Field investigation, Analytic studies, Evaluation, and Linkages. Policy development [recently added].

20. Knowledge required by Epidemiologists Public health , because of the emphasis on disease prevention. Clinical medicine , because of the emphasis on disease classification and diagnosis.   Pathophysiology , because of the need to understand basic biological mechanisms in disease.

21. Knowledge required cont’d… Statistics , because of the need to quantify disease frequency and its relationships to antecedents. Social sciences , because of the need to understand the social context in which disease occurs and presents.

22. Scope of Epidemiology • Epidemics • Non-communicable diseases. • At present epidemiologic methods are being applied to: – Infectious and non infectious diseases – Injuries and accidents – Nutritional deficiencies – Mental disorders – Maternal and child health – Congenital anomalies – Cancer – Occupational health – Environmental health – Health behaviors 8/9/2023 22 All disease conditions & related events

23. SCOPE OF EPIDEMIOLOGY : Since 5 th century Middle of 20 th century Past 25 yrs recently Epidemic of communicable diseases Endemic communicable diseases & Non communicable diseases Chronic diseases, injuries, birth defects MCH Occupational health Env’tal health Health related behavior Genetic markers of disease risks ▲ + ▲ + ▲ + ▲+

24. Fields of Epidemiology – Define the following fields Microbial/Infectious epidemiology Descriptive epid Surveillance epid Global epidemiology Testimonial epid Entrepreneurial epid Big Epidemiology Genetic epid Molecular epid Social epid Clinical epid “Risk factor” epid 8/9/2023 24

25. Epidemiology Fields Surveillance epidemiology (outbreak investigations), and epidemic control Descriptive epidemiology – examination of patterns of occurrence of disease and injury and their determinants Microbial/Infectious epidemiology – biology and ecology of pathogenic microorganisms, their lifecycles, and their interactions with their human and non-human hosts 8/9/2023 25

26. Epidemiology Fields “Risk factor” epidemiology – searching for exposure-disease associations that may provide insights into etiology and avenues for prevention Clinical epidemiology and the evaluation of healthcare – assess accuracy, efficacy, effectiveness, and unintended consequences of methods of prevention, early detection, diagnosis, treatment, and management of health conditions Social epidemiology – interpersonal and community-level factors influencing health at the population level 8/9/2023 26

27. Epidemiology Fields Molecular epidemiology – investigate disease at the molecular level to precisely characterize pathological processes and exposures, to elucidate mechanisms of pathogenesis, and to identify precursor conditions Genetic epidemiology – the confluence of molecular biology, population studies, and statistical models with an emphasis on heritable influences on disease susceptibility and expression Big Epidemiology – multisite collaborative trials, such as the Hypertension Detection and Follow-up Program (HDFP), Multiple Risk Factor Intervention Trial (MRFIT), Women’s Health Initiative (WHI) 8/9/2023 27

28. Epidemiology Fields Entrepreneurial epidemiology – building institutions and careers by winning research funding and facilities Testimonial epidemiology – giving depositions and testifying in court or in legislative hearings on the state of epidemiologic evidence on a matter of dispute Global epidemiology – assessing the effects of human activity on the ecosystem that supports life on Earth. 8/9/2023 28

29. BASIC ASSUMPTIONS IN EPIDEMIOLOGY A . “Disease occurrence in human population is not random” – Disease is not randomly distributed throughout a population – Epidemiology uses systematic approach to study the differences in disease distribution in subgroup – Why certain individuals/group acquire disease and others not ?

30. B. “Human disease has causal and preventive factors that can be identified through systematic investigation of different population or sub group of individuals within a population at different place or time”. – Allows for study of causal and preventive factors

31. History of Epidemiology (460-377 B.C) Epidemiological thinking traced to the time of Hippocrates /5th century B.C., but the discipline did not flourish until the 1940s . In 400 B.C. he attempted to explain disease occurrence from a rational instead of a supernatural viewpoint on his three books Epidemics I, Epidemics III, and on Air, Waters and Places Hippocrates - 5th century B.C.- the father of modern medicine and the first Epidemiologist

32. For the first time, he suggested that the development of human disease might be related to the external as well as personal environment of an individual

33. Whoever wishes to investigate medicine; should proceed thus : – Season of the year – The wind – The water – The earth – Drinking and eating pattern of the people – Exercise and labor

34. John Graunt /1662 • The most important advances in epidemiology is attributed to the English man John Grant (1620 – 1674). – His research laid the groundwork for both epidemiology and demography . - He wrote his work as “Natural and Political Observations…Upon the Bills of Mortality” , which was first published in England in 1662 ”

35. – He was the first to quantify patterns of birth, death and disease occurrence , noting male-female disparities, high infant mortality, urban-rural differences, and seasonal variations • Seasonal variation for mortality • Assessed the impact of plague

36. James Lind/1747 - he used an experimental approach to prove the cause of scurvy by showing it could be treated effectively with fresh fruit • Designed first experiments to use a concurrently treated control group

37. William Farr/1839 - an English physician, established the tradition of application of vital statistical data for the evaluation of health problems.

38. Examined mortality, occupation and marital status Defined: population at risk Choosing appropriate comparison group Considered other factors: • Age, • Duration of exposure, • General health status He was considered the father of modern vital statistics and surveillance ,

39. • He developed many of the basic practices used today in vital statistics and disease classification • He extended the epidemiologic analysis of morbidity and mortality data, looking at the effects of marital status, occupation , and altitude.

40. Edward Jenner (1749-1823) Pioneered clinical trials for vaccination to control spread of smallpox Jenner's work influenced many others, including Louis Pasteur who developed vaccines against rabies and other infectious diseases

41. John Snow/1853: an English physician formulated and tested a hypothesis concerning the origin of an epidemic of cholera in London. Snow postulated & demonstrated that cholera was transmitted by drinking contaminated water. Careful mapping of cholera cases in London during cholera epidemic

42. – Lambeth , Southwark and Vauxhall Company (1949 – 1954) polluted by the sewage from London. – Lambeth changed the source • Rate of Cholera declined in the area supplied – Southwark and Vauxhall Company continued

43. Evolution of modern Epidemiology Milestones have been broadly divided into four stages • Sanitary statistics • Infectious disease epidemiology • Chronic disease epidemiology and • Multi-level causality

44. The Era of sanitary statistics Common in the first half of the19th century The widespread etiologic theory was "miasma” i.e., poisoning by polluted emanations from soil, air, and water Focused on assessing the clustering of morbidity and mortality and on preventive measures such as drainage, sewage, and sanitation Focused on the environment: the theory that all diseases were due to bad air (contaminations-miasma)

45. The Era of infectious disease epidemiology Late 19th C - first half of the 20th C The germ theory prevailed It was the “Period of bacteriology” Analytic approach -laboratory isolation and culture Preventive approach: -interrupt transmission of the infectious agent

46. The Era of chronic disease epidemiology Since World War II Focused on risk factors at individual levels The "black box" approach: exposures are related to outcomes without always understanding the intervening factors or pathogenesis

47. Primary analytic methods were used:- risk ratios to relate exposures to outcomes. Preventive measures:- control of risk factors by modifying the environment or human behavior (e.g., smoking, physical inactivity )

48. Multi-level causality • Multiple risk factors interacting to cause disease including molecular pathogenesis of diseases • The focus was on risk factors as well as causal pathways at the community level and the pathogenesis at the individual level

49. Features of Epidemiology Studies are conducted on human population Ethical issues: tending to observational studies Examines patterns of events in groups of people Can establish cause and effect relationship without the knowledge of biologic mechanism - Smoking and lung cancer Covers a wide range of conditions From infectious to non-infectious From simple survey to complex drug trials

50. Major approaches in Epidemiology Descriptive epidemiology Analytic epidemiology

51. Descriptive epidemiology • One of the basic types of Epidemiology which is concerned with describing: • the frequency and distribution of diseases and other health related conditions by time, place, and person . • It provides valuable information: to allocate resources and plan effective prevention or education programs It provides the first important clues about possible determinants of a disease (formulation of hypothesis)

52. Major characteristics in Descriptive Epidemiology Person , Place and Time . • For the full description of the occurrence of a disease, the following questions must be considered . • Who is affected? • Where? and • When do the cases occur? • How many?

53. Person • People can be categorized with respect to many demographic and personal variables such as: • Age • Sex • Religion • Education • Ethnic group and Race • Other personal variables

54. Place: it refers to region, residence, workplace, topography, or location of rooms, buildings or other structures 1. Natural barriers Environmental or climatic conditions, such as temperature, humidity , rainfall, altitude, mineral content of soil, or water supply . helpful to see the nature and aetiology of diseases.

55. 2. Political boundaries . - intended for planning and allocation of resources 3. Urban-rural differences in disease occurrence in terms of migration , living style and differential environmental exposures .

56. Time: it refers to seasonal patterns, secular trends, or acute changes in disease occurrence There are three major types of changes in disease occurrence over time. 1. Secular/slow Trends Years or decades. E.g. AIDS, Lung Cancer 2. Periodic or cyclic changes ; which refers to recurrent alterations in the frequency of diseases. Cycles have some periodicity (e.g. annual) Malaria , meningitis 3. Sporadic –at irregular and unpredictable intervals.

57. Analytic Epidemiology It involves explicit comparison of groups of individuals to identify determinants of health and diseases . Testing of hypotheses, which in turn may arise from Case reports Case series Laboratory studies Descriptive epidemiologic studies

58. It focuses on determinants of disease by testing hypothesis. – Try to answer questions like “why” and “how” of a disease The key to epidemiologic analysis is comparison group

59. Purpose/ Aim of analytic Epidemiology 1. To search for cause and effect : Why?? How?? 2. To test hypothesis about causal relationship 3. To quantify the association between exposure and outcome- Measure of association

60. • Many studies have both descriptive and analytic aspects data collected in one mode may end up being used in the other as well . Whether a particular study is primarily “descriptive” or “analytic ” may be a matter of the investigator’s stance in relationship to the study question and data collection . • Due to this descriptive and analytic classification is a continuum than being a dichotomy.

61. Epidemiologic Concepts Community- refers to a group of people who share some thing in common . E.g. common denominators can be neighborhood, work place, race, religion or social activity . Communities - engaged in activities that demand interrelationship of efforts, they give rise to shared culture, and they are often sited in a particular geographic location.

62. Community vs Clinical medicine : Community medicine - is a system of delivery of comprehensive ( preventive , social medicine, along with curative and promotive ) health care to the people by a health team to improve the health of a community

63. Also concerned with diagnosing the health problems of a community , and with planning and managing community health services • Here (community medicine), the community replaces the individual patients as the primary focus of concern

64. It helps to evaluate the health of a defined community including those members who would benefit from, but could not seek medical care • These approach requires techniques and skills in addition to those needed for clinical practice Clinical medicine:- medical care of individuals. • Typically these are sick people who have presented for help.

65. Public health - a science and art of preventing disease , prolonging life, and promoting health and efficiency through organized community effort for sanitation, control of communicable disease, health education (Winslow, 1920) Is saving life as group/community/population

66. Public health is: Preventing disease Prolonging life Improving quality of life Eliminating health inequalities Organizing community to promote active participation

67. Core functions of Public Health 1. Assessment- of health need, by conducting surveillance and specific studies 2. Leadership - program design, resource allocation and social mobilization 3. Provision of services- assure availability of quality and comprehensive health services through accessible outlets

68. Information on the health and disease of a defined community is gathered through Community Diagnosis . Community Diagnosis - the process of identification and detailed description of the most important health problems of a given community. It may be broad or narrow in scope, and may deal with only a single topic or a single sub group.

69. Some of the ways to make community diagnosis are: Discussion with community leaders and health workers Survey of available health records Field survey. Compilation and analysis of the data . It is impossible to address all the identified problems at the same time because of resource scarcity. Therefore the problems should be put in the order of priority using a set criterion.

70. Community diagnosis provides basis for decision on: – The need for intervention – Type of intervention needed – Target group at whom intervention should be directed – Provide baseline for later intervention

71. Preventive medicine:- deals with the measures to protect the individuals from the diseases, and to keep them in a state of positive health

72. Social medicine: – is a study of man as social being in relation to his environment It is a branch of medical science dealing with the study of community health with respect of social aspects ( social, economical , cultural, psychological, environmental and genetic factors ) in the community as a whole Epidemiological and statistical aspects are also dealt with.

73. Criteria for priority setting Magnitude (amount or frequency) of the problem Severity (to what extent is the problem disabling, fatal) Feasibility (availability of financial and material resource, effective control method) Community concern (whether it is a felt problem of the community ) Government concern (policy support, political commitment)

74. Risk Factors: • any factor associated with an increased or decreased occurrence of disease. • A factor associated with an increased occurrence of a disease is risk factor for the exposed group; and a factor associated with a decreased occurrence of a disease is a risk factor for the non exposed group.

75. Risk factors could be: Factors related to the agent: Strain difference Factors related to the human host: Lack of specific immunity. Factors related to the environment: Overcrowding, Lack of ventilation

76. Risk factors may further be classified as: • Factors susceptible to change: smoking habit, alcohol drinking habit • Factors not amenable to change: age, sex, family history In order to be able to prevent disease, it is vital to identify factors that can be changed.

77. For some diseases, the specific causes are not known . In such cases it is very important to identify risk factors, especially those that can be changed and act on them. Epidemiology is mainly interested in those risk factors that are amenable to change as its ultimate purpose is to prevent and control disease and promote the health of the population .

78. Disease- is a physiological/psychological dysfunction • Illness- a subjective state of the person who feels aware of not being well • Sickness- is a state of social dysfunction that is a role that the individual assumes when ill

79. presentation Assignment The epidemiological concept of population

80. THANK YOU FOR YOUR ATTENTION!