Epidemiology. Muhammad Tahir, MPH,MSc E&B. Acknowledgments: Yasmin Parpio Shair Muhammad

Transcription

1 Introduction to Epidemiology Muhammad Tahir, MPH,MSc E&B Acknowledgments: Yasmin Parpio Shair Muhammad 1

2 Objectives By the end of this session, the students will be able to: Define the term Epidemiology. State the major objectives of Epidemiology. Discuss the various models employed in the field of Epidemiology Explain the stages of Natural History of Diseases. Identify the three levels of prevention. 2

3 Definition of Epidemiology Epi : Demos: Upon People Logy: Knowledge It is the study of how disease is distributed in population and of the factors that influence or determine this distribution (Gordis,1996) 3

4 Definition of Epidemiology Study of disease and other health-related phenomena in groups of persons (Kramer,1990) The study of the distribution and determinants of health related states in specified populations and the application of this study to control health problems." 4

5 Goals / Aims of Epidemiology i Scientific research is the process of suggesting the relationship between cause and disease in a field that may be or not related to public health 5

6 Goals / Aims of Epidemiology i Evaluation research is concerned with the decision making process to implement the new strategies, continue the implemented strategies that may be or not in the public health field To minimize or eradicate the disease To prevent the re-occurrence 6

7 Uses of Epidemiology To provide a clue to changes taking place over time " To identify subgroups in the population who are at high h risk for disease." To determine the best or most appropriate types of primary and secondary prevention.' o Primary prevention prevents disease in the well individual. id Example: vaccination. o Secondary prevention limits disease by early detention usually through screening programs 7

8 Epidemiology & Prevention Why should we identify risk groups o To identify risk groups and to identify the associated specific factors or characteristics ti that put them in the risk group. o Early identification of disease through screening program to prevent the burden of disease on the risk group and to be able to provide the best available intervention 8

9 Specific Objectives of Epidemiology To identify the causes of disease and the risk factors To identify the extend of the disease found in the community To determine the health status of population To study natural history and prognosis of disease To evaluate new preventive and therapeutic measures and new modes of health care delivery. To provide the foundation for developing public health and regulatory decisions relating to environmental problems. 9

10 Components of Epidemiology Descriptive Epidemiology Identifying both pattern and frequency of health related events Analytical Epidemiology Focuses on determinants of health outcomes 10

11 Cycle of Epidemiologic Analysis 11

12 Epidemiological Triad The cause of any disease whether communicable or noncommunicable are determined by the interactions between the agent, the host and the environment. Agent Environment Host Ansari MA,

13 Epidemiological Triad 13

14 The Agent Is an organism or substance, the presence or lack of which may initiate disease process. Classification of Agent Living or Biological Non Living onutrients Fats, Vitamins, minerals etc. ochemical Lead, Arsenic, Alcohol etc. ophysical obacteria ofungi oprotozoa P t Atmospheric oviruses etc. pressure, Radiation, Sound, Vibrations etc. 14

15 Host Environment The Host is the man himself and his characteristics. e.g. age, sex, and race (ethnicity) socio economic status, life style. Acts as a reservoir for theagents of disease. 15

16 The Host Environment Interaction Virtually all chronic diseases have multi factorial etiologies many may have infectious components. Enteroviruses Epstein Barr virus Chlamydia pneumoniae Helicobacter pylori Hepatitis B and C Borna disease virus Type I diabetes B-cell lymphomas Heart disease Peptic ulcers Liver cancer Schizophrenia 16

17 Wheel Model Wheel model is another approach to depicting human environment relations. o Definition: The wheel consists of a hub that represents the host with all of its human characteristics such as genetic make up, personality, and immunity. The surrounding wheel represents the environment and comprises of biological, social and physical dimensions. o The relative size of each component in the wheel depends on the health problem being analyzed. (Mary To Clark, 1992) 17

18 Wheel Model Genetic core Mausner, J. S. & A. K. Bahn Epidemiology. Sanders, Philadelphia. 18

19 Ecological model of Alcoholism 19

20 Classification Physical: Is the space around man containing gases (air) liquids (water) and solids. Biological: All living things that surrounds man. Both animals and plants. Social: The customs, habits, culture, education and the living standards. 20

21 The Web Of Causation o The web of causation views a health condition not a the result of individual factors, but of complex interrelations among multiple factors i.e. one factor may lead to others, which in-turn lead to others, all of which may interact with one another to produce the health condition. Features: o It also includes environment, host, and agent factors. o It allows for interaction between different components. o It suits chronic diseases and environmental effects. 21

22 Web Of Causation 22

23 Phases of Epidemiology Descriptive Epidemiology: o It is concerned with disease distribution and frequency. It asks: what is the problem its frequency, who is involved. Where and when. Analytical lepidemiology: o Attempts to analyze the causes or determinants of diseases by testing hypotheses. By asking how and why questions. 23

24 Phases of Epidemiology Experimental Epidemiology: Used to answer questions about the effectiveness of new methods for controlling disease or for improving under lying conditions. Evaluation Epidemiology: It attempts to measure the effectiveness of different health services and programs. 24

25 Epidemiological Approach The information required can be approached through a series of questions. What Who Where When How Why Is the health program/disease? Wh Is affected age, sex, and social class? Does the problem occur? When In terms of days, months, seasons, and years? Health Problem occurs, specific causative agent? Does it occur, reasons for its occurrence? 25

26 Series of Questions What is the health problem? Who is affected, with reference to age, sex, social class, ethnic group, occupation, heredity and personal habits? Where does the problem occur, in relation to place of residence, geographical distribution ib ti and place of exposure? When does it happen, in terms of day, months, seasons or years? How does the health problem or disease occur? Why does it occur, in terms of the reasons for its persistence or occurrence? What interventions have been implemented as a result of the information gained and what was their effectiveness? Have there been any improvements in health status? 26

27 Natural History of Disease Onset of Exposure symptoms Pathologic changes Usual time of diagnosis Stage of susceptibility Stage of subclinical disease Stage of clinical disease Stage of recovery, disability or death Primary Prevention Secondary Prevention Tertiary Prevention 27

28 The Natural History of Disease Stage 1: Susceptibility Description: Risk factors which h assist the development of disease exist, but disease has not developed Example: Smoking 28

29 The Natural History of Disease (cont d) Stage 2: Description: Pre-symptomatic disease Changes have occurred to lead toward illness but disease is not yet clinically detectable Example: Alveoli deteriorate 29

30 The Natural History of Disease (cont d) Stage 3: Clinical Disease Description: Detectable signs and/or symptoms of disease exist Example: Emphysema detected by pulmonary function test 30

31 The Natural History of Disease (Cont d) Stage 4: Disability Description: Disease has progressed to the point of causing a residual effect Example: Person has difficulty breathing 31

32 Levels of Prevention Level: Description: Example: Primary Promote general health and avoid risk factors for disease --- Utilize protective measures to prevent susceptibility and pre-symptomatic disease Stop smoking or choose not to start; avoid areas where people are smoking 32

33 Levels of Prevention Level: Description: Example: (Cont d) Secondary Early detection and timely treatment Routine pulmonary function tests for those at risk; medicine to help patients breath more easily; smoking cessation programs if patient smokes 33

34 Levels Of Prevention (cont d) Level: Description: Example: Tertiary Rehabilitation and prevention of further disease or disability Oxygen therapy; facilitating ambulation with technical devices 34

35 Prevention Approaches Population Based Approach: Preventive measure widely applied to an entire population p (public health approach) Strive for small absolute change among many persons Must be relatively inexpensive and noninvasive 35

36 Prevention Approaches High Risk Approach: Target group of individual at high risk Strive for strong risk factor control Often times requires clinical action to identify the high risk group and to motivate risk factor control. 36

37 Levels of Prevention Primary Prevention Prevention of disease by controlling risk factors (e.g., non-smoking promotion) 37

38 Levels of Prevention Secondary Prevention Reduction in consequences of disease by early diagnosis and treatment (e.g., cervical cancer screening) 38

39 Levels of Prevention Tertiary Prevention Reduction in complications of disease (e.g., MV crashes and ICU) 39

40 40

41 Group Assignment Group 1 : Epidemiological Triad for Scabies Group 2: Wheel Model for Drug addiction e.g. Cannabis Group 3: Web of Causation of Malnutrition Group 4: Natural History of Hypertension Group 5: Level of Prevention for IHD [Ischemic heart Disease] 41