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- 2. 2 Introduction • The term epidemiology is derived from the Greek word epidemic. – Epi means-Among, upon, – Demos means study population or people and – Logos means scientific study. • So – it is the scientific study of the disease pattern in human population. – In broad sense, it is the study of effects of multiple factors on human health. – It is multidisciplinary subject involving those of the physician, Biologists, Public Health experts, Health educators etc.
- 3. Definitions • The science of infective diseases, their prime causes, propagation and prevention. (Stallbrass 1931.) • The science of the mass phenomena of infectious diseases or the natural history of infectious diseases. (Frost 1927) 3
- 4. Definitions • The study of the disease, any diseases, as a mass phenomenon. (Greenwood 1935) • The study of condition known or reasonably supposed to influence the prevalence of disease. (Lumsden 1936) • Epidemiology as, study of the distribution and determinants of diseases frequency in man. (Mac Mohan and Pugh) 07/30/14 4
- 5. The widely accepted definition of epidemiology is, • "The study of the distribution and determinants of health related states or events in specified population and the application of the study to control of health problems“ (J.M. Last 1988) 07/30/14 5
- 6. Basic Tenets of epidemiology • 07/30/14 6 Target of a study in epidemiology is human Population as Geographical area, Age, Sex, Ethnicity, Race etc.: the most common population in epidemiology is the population is a given area or country at a given time. Since the structure of population varies at each time such variations also have to be taken in to consideration during data analysis. • Allfindings must relate to the defined population. Enumeration is not enough in epidemiology, the population at risk of developing that diseases need to be enumerated as well.
- 7. Basic Tenets of epidemiology • Conclusions are based of comparisons: comparing the rates of diseases frequency among the exposed and unexposed and the unexposed is an important epidemiological method. • Description of events by time, place and person. Getting answer for when, where and who are affected is very important in epidemiology to formulate hypothesis about its causation. Other important aspects are what, why and how of the events. 07/30/14 7
- 8. Aims of Epidemiology According to the International EpidemiologicalAssociation (IEA) Epidemiology has three main aims. – To describe and analyze diseases occurrence and distribution in human populations; – To identify etiological factors in the pathogenesis of diseases; – To provide the data essential to the planning, implementation and evaluation of services for the prevention, control and treatment of diseases and to the setting up of priorities among those services. 07/30/14 8
- 9. The ultimate aims of epidemiology can be concluded in to two followings points. • To eliminate or reduce the health problem or its consequences and • To promote the health and wellbeing of society as a whole. 07/30/14 9
- 10. Uses of epidemiology • Investigationof causationof disease. GeneticFactors Good Health IllHealth Environmental Factors 07/30/14 10
- 11. Uses of epidemiology • Studyof thenaturalhistoryandprognosisof diseases. Goodhealth Subclinical Changes Clinical Diseases Death Recovery 07/30/14 11
- 12. Uses of epidemiology • 12 Description of the health status of the populations. It includes proportion with ill Health, change over time, change with age etc. • Evaluation of the interventions. • Planning health services, Public policy and programs.
- 13. Cont.. • To study the natural history of disease, disability, injury and death • To make a community diagnosis • To complete a clinical pictures • To identify syndromes • To search for causes of health and disease
- 14. And, Recently 14 • epidemiologists have become involved in evaluation the effectiveness and efficacy of health services, by determining the appropriate length of stay in hospital for specific conditions, the value of treating High blood pressure, the efficiency of sanitation measures to control diarrhoeal diseases, the impact on public health of reducing lead activities in petrol etc.
- 15. Components of epidemiology Diseasefrequency: - • The core characteristics of epidemiology are to measure the frequency of diseases, disability or death in a specified population. it is always as the rate, ratio and proportion. • Much of the subject of epidemiology subject matter of measurement of diseases and health related events falls in the domain of biostatistics, which is a basic tool of epidemiology. This helps to development of strategies for prevention or control of health related problems. 07/30/14 15
- 16. Componentsof epidemiology Distribution of diseases: - • • 07/30/14 16 • Health events occur in pattern in community and this pattern varies from community to community. Also health events or diseases condition affect population at various age groups, different sexes, different subgroups of population. Distributions of events are based on time, place, and person. We can analyze whether any increases or decreases occur for a particular condition. Epidemiology addresses itself to a study of these variations or patterns, which may suggest or lead to measure to control or prevent the diseases. An important outcome of this study is formulation of etiological hypothesis.
- 17. Componentsof epidemiology Determinants of diseases;- • Epidemiology helps in identifying the causative agent or the risk/predisposing factors of 07/30/14 17 • diseases . This is one of the real uses of epidemiology. Understanding the factors leading to any programs for the control of those diseases.
- 18. History of epidemiology • 07/30/14 18 • • The history of epidemiology has its origin in the idea, goes back to (400BC) Hippocrates through John Graunt (1662), William Farr, John Snow and others that environmental factors can influences the occurrences of diseases in stead of supernatural viewpoint of diseases. John Graunt analysis and published the mortality data in 1662.He was the first quantify pattern of death, birth and diseases occurances. No one built upon Graunt’s work until 1800’s.when William Farr began to systematically collect and analyst the Britain’s mortality statistics. Farr considered as the father of vital statistics and diseases classifications.
- 19. History of epidemiology • Meanwhile John Snow was conducting the series of investigations in London that later earned him the title father of field epidemiology. Snow conducted his classical study in 1854 when an epidemic of cholera developed in the golden square of London. During the time of microscope development, snow conducted studies of cholera outbreak both to discover the causes of diseases and prevent its recurrences. • During that time two men (Farr and snow) had major disagreement about the cause of cholera. Farr adhere to what was the called miasmatic theory of diseases, according to this theory which was commonly held at a time diseases was transmitted by a miasma or cloud that clung low on the earth surface. 07/30/14 19
- 20. History of epidemiology • However Snow did not agree he believed that cholera is transmitted through contaminated water. He began his investigation by determining where in this area person with cholera lived and worked. He then used this information to map for distribution of diseases. Snow believed that water was the source of infection for cholera. He marked the location and searches the relationship between cases and water sources. He found that cholera was transmitted though contaminated water. This was the major achievement in epidemiology. 07/30/14 20
- 21. History of epidemiology • In the 1900s epidemiologists extend their methods to noninfectious diseases and studied effect of behaviors and life style in human health. There are some important achievements in epidemiology they are; – John Snow and cholera epidemic in London in 1848-1854. – Framingham heart study started in 1950 in Massachusetts, USAand still continuing to identify the factors leading to the development of the coronary heart diseases. – Smoking and lung cancer by Doll and Hill in 1964. – Polio Salkvaccine field trial in 1954 to study the protective efficacy of vaccine in a million school children. – Methyl Mercury poisoning 1950s In Minamata 07/30/14 21
- 22. Field of epidemiology Epidemiology covers the various types of field in different types of activities. It is applied in every field as agricultural, economics, statistics etc. They are as • • • • • • • • 07/30/14 22 Clinical epidemiology Geographical epidemiology Social epidemiology Statistical epidemiology Descriptive epidemiology Analytical epidemiology Experimental epidemiology Infectious diseases epidemiology etc.
- 23. Comparison between Clinical medicine and Epidemiology 23 Area Epidemiology Clinical Medicine Population ( Defined or at risk) S. N. 1 Unit of study 2 objectives Cases or case To identify the source, Mode of To cure the patient. transmission, etiological factors, Group of people or community Sick and healthy By survey, research Experts goes to community 3 Examination 4 Concern with 5 Diagnosis 6 Where to go? 7 Area concern Individual case Sick Individual test done. Patient goes to hospital Mainly in curative field Mainly concern to preventive and promotive through intervention Bio-statistical of By tables, charts and diagrams Bio-medical By laboratory and others reports Long process 8 Concept 9 Presentation result 10 Time 11 outcome implementation and health Planning, promotion Short time sometimes long time Cured or disability or death
- 24. Conceptofdisease causation 24 • Germtheoryof diseases • Epidemiological triads • Multifactorialcausation • Webof causation
- 26. Germ theory According to this theory, there is one single specific cause of every disease. This refers to one to one relationship between the causative agent and disease.
- 28. Epidemiologicaltriads 07/30/14 28 • Agent-Biological,chemical,physical,nutritional, Social • Host factor- Age, sex, heredity, nutrition, Occupation, Custom, habits, Immunity power, Biological-Blood sugar, Cholesterol, Housing,Maritalstatus,socio-economicstatus • EnvironmentalFactor-Physical,Biological,Psychosocial
- 34. Multifactorial Causation Theory Epidemiological theory is not applicable for non infectious and chronic diseases like coronary artery diseases etc. because it has many causes or multiple factors. This theory helps to understand the various associated causative factors, prioritise and plan preventive and plan measures to control the disease.
- 36. Webs of Causation Given by macmohan and pugh. according to him – disease never depends upon single isolated cause rather it develops from a chain of causation in which each link itself is a result of complex interaction of preceding events these chain of causation which may be the fraction of the whole complex is known as web of causation.
- 38. DEVERS EPIDEMIOLOGICAL MODEL This model is composed of four major categories of factors - human biology - lifestyle, - environment and - health system. all these factors influence health status positively or negatively. -Human biological --- epidemiological triad and include genetic inheritance, complex physiological systems, factors related to maturation and ageing -Life style factors include daily living activities, customs, traditions, health habits etc Environmental factors include physical, biological, social and spiritual components Health care system factors include availability, accessibility, adequacy and use of health care services at all levels.
- 39. Dynamicofdiseases Transmission • Sourceof Infection orreservoirof infection • Modeof transmission • SusceptibleHost 39
- 40. Reservoirof infection 40 • Human reservoir •Case– Clinical,Subclinical, Latent •Carrier-Incubatory ,Convalescent, Healthy • AnimalReservoir– Zoonotic • Reservoirof non-living Things-Soil • Sourceof Infection-Secretion/Excretionof reservoirs,Sometimes Reservoirs
- 41. ModeofDiseases transmission 07/30/14 41 • Direct • DirectContact • Droplet Infection • Inoculationintoskinor mucosa • Contactwithinfected Soil • Vertical • Indirect • Vehicleborne disease • VectorBorne disease – Biological – Mechanical • AirBorne Disease – Droplet Nuclei – Infective Dust • Fomite • Fingers
- 42. SusceptibleHost Lowimmunityperson.Highriskperson • Portalof entry Modeof Transmission • Suitable Places • Develop/ Multiplication/Disease/Carrier • Portalof exit • Respiratory • Gastrointestinal • Urinary • Skin • BodyFluids 07/30/14 30
- 43. Method or Approaches of Epidemiology 1. Descriptive method 2. Analytical method 3. Experimental method
- 44. Descriptive method Data are collected about: 1. Personal characteristics 2. Place distribution 3. Time distribution / Trends Provide Information: 1. Data for describing the nature of diseases 2. Clues to etiology of disease 3. Background information for planning
- 45. Types of Descriptive methods 1. Cross sectional Studies 2. Longitudinal studies
- 46. Analytical method 1. Case control study 2. Cohort study - Prospective cohort study - Retrospective Cohort Study - A combination of retrospective and prospective cohort study
- 47. Experimental Method 1. Helps to confirm the etiology 2. Establish the efficacy of preventive or therapeutic measures 3. Helps to evaluate health care services. 4. Studies are done under controlled conditions.
- 48. Diseasespreventionand control 07/30/14 48 • Preventionof sourceorreservoir • Early diagnosis • Notification • EpidemiologicalInvestigation • Isolation • Treatment • Quarantine • Interruptionof thedisease transmission • Preventionof susceptible host • Immunization • Healtheducation
- 49. EpidemiologicalInvestigation 07/30/14 49 • Verificationof diagnosis • Confirmationof theexistenceof anepidemic • Definingthepopulationatrisk • Obtainingthemapof thearea • Countingthe population
- 50. Continue 07/30/14 50 • Rapidsearchforallcasesandtheircharacteristics • • • MedicalSurvey Epidemiologicalcasesheet Searchingformore cases • Dataanalysis • • • Time Place Person • • • • • Formulationof hypothesis Testingof hypothesis Evaluationof ecological factors Furtherinvestigationof populationatrisk Writingthe report