1 / 27

Epidemiologic Triads & Natural History of Disease

Epidemiologic Triads & Natural History of Disease. Dr. Salwa A. Tayel & Dr. Mohammad Afzal Mahmood KSU Department of Family & Community Medicine September, 2013. OBJECTIVES OF THE LECTURE. By the end of this lecture students will be able to:

ash
Télécharger la présentation

Epidemiologic Triads & Natural History of Disease

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Epidemiologic Triads & Natural History of Disease Dr. Salwa A. Tayel& Dr. Mohammad Afzal Mahmood KSU Department of Family & Community Medicine September, 2013

  2. OBJECTIVES OF THE LECTURE By the end of this lecture students will be able to: • Explain epidemiologic triads as a model of study of disease causation • Describe natural history and spectrum of infectious diseases and their implications for public health. Triads & Natural History 2

  3. Concepts • Descriptive epidemiological triad • Analytical epidemiological triad • Natural history of disease • Spectrum of disease • Public health implications Triads & Natural History

  4. Purpose of studying causal models Studying how different factors can lead to ill health generates knowledge for disease prevention & control The classic epidemiological triangle or triad help understand the relation between a disease, disease causing agent and environment 4 Triads & Natural History

  5. Epidemiological Triads Descriptive Epidemiology Triad: • Person • Place • Time Analytical Epidemiology Triad: • Agent • Host • Environment Triads & Natural History

  6. Descriptive Epidemiology Descriptive Epidemiology is a Necessary Antecedent Of Analytic Epidemiology To undertake an analytic epidemiologic study you must first: • Know where to look • Know what to control for • Be able to formulate hypotheses, compatible with laboratory evidence Triads & Natural History

  7. Person • Age • Gender • Marital status • Ethnicity/Race • Behavior / life-style factors • Socio-economic status • Education • Occupation • Income • Biological factors, passive/active immunity, concomitant illness Triads & Natural History

  8. Place • Geographically restricted or widespread (pandemic)? • Relation to water or food supply (clusters: multiple / one) • Residence (rural, urban, remote) • Climate (temperature, humidity) Triads & Natural History

  9. Time • Changing or stable? • Seasonal variation. • Clustered (epidemic) or evenly distributed (endemic)? • Point source or propagated. Triads & Natural History

  10. Time Trends • Point source e.g. food-borne outbreaks), in terms of hours / days • Seasonal - cyclicity (e.g. common cold, influenza), in terms of months • Propogative (e.g. water borne epidemics), in terms of weeks / months • Secular(e.g. morbidity / mortality of non-communicable diseases), in terms of years • Cluster in time / place Triads & Natural History

  11. The Basic Triad Of Analytic Epidemiology THE THREE PHENOMENAASSESSED IN ANALYTIC EPIDEMIOLOGY ARE: HOST AGENT ENVIRONMENT

  12. The Analytical Epidemiologic Triad This model comprises a susceptible host (the person at risk for the disease), a disease agent (the proximate cause), and an environmental context for the interaction between host and agent. Thus, development of disease is a combination of events: A harmful agent A susceptible host An appropriate environment Triads & Natural History

  13. Agents Biological (micro-organisms) Physical(temperature, radiation, trauma, others) Chemical(acids, alkalis, poisons, tobacco, medications / drugs, others) Environmental(nutrients in diet, allergens, others) Nutritional (under- or over-nutrition) Psychological experiences Triads & Natural History

  14. Host Factors • Host factors are intrinsic factors that influence an individual’s exposure, susceptibility, or response to a causative agent. These include: • Genetic endowment • Immunologic state • Personal behavior (life-style factors): diet, tobacco use, exercise, etc • Personal characteristics (described before, under “person”), including: age, gender, socio-economic status, etc. Triads & Natural History

  15. Environmental factors are extrinsic factors which affect the agent and the opportunity for exposure. These include: Physical factors: e.g. geology, climate (temperature, humidity, rain, etc) Biologicalfactors: e.g. insects that transmit an agent Socioeconomic factors: e.g. crowding, sanitation, and the availability of health services Phenomena which bring the host and agent together: vector, vehicle, reservoir, etc Environment Triads & Natural History

  16. Summary of Analytical Triad • Agent factors include infectious microorganisms, e.g. virus, bacterium, parasite, or other agents. • They may be necessary but not always sufficient alone to cause disease. • Host factors are intrinsic factors that influence an individual’s exposure, susceptibility, or response to a causative agent • Environmental factors are extrinsic factors which affect the agent and the opportunity for exposure. 16 Triads & Natural History

  17. Example The number of people who become diseased with tuberculosis will depend on: • characteristics of the agent, • environmental factors, • And host factors Explain some of these factors Triads & Natural History

  18. The Analytical Epidemiology Triad Host: Intrinsic factors, genetic, physiologic factors, psychological factors, immunity Health or Illness ? Agent: Amount, infectivity, pathogenicity, virulence,…. Environment: Physical, biological, social 18 Triads & Natural History

  19. Natural History of Disease

  20. Natural history of disease Naturalhistoryof disease refers to the progress of a disease process in an individual over time, in the absence of intervention. The natural history of a disease describes the course of the disease in an individual starting from the moment of exposure to the causal agents till one of the possible outcomes occurs. 20 20 Triads & Natural History

  21. Natural history Phenomena • Induction : time to disease initiation • Incubation:– time to symptoms (infectious disease) • Latency: time to detection (for non-infectious disease) or to infectiousness Triads & Natural History

  22. Natural history of disease 22 22 Triads & Natural History

  23. Natural history of disease 23

  24. Point of Exposure Onset of symptoms Screening Natural History of Disease Detectable subclinical disease Clinical Disease Outcome: Stage of Recovery, Complications, Disability, or Death Subclinical Disease Susceptible Host Diagnosis sought Triads & Natural History

  25. The problem • The problem is that we might know about disease onset when symptoms occur but most likely we will only know about the disease when a person seeks care for the symptoms. • In some situations an investigator will only become aware of a case after a diagnosis is made. Triads & Natural History

  26. Importance of studying Natural history of disease • The understanding of this progression from disease onset to cure or death is important for epidemiologists. • Natural history is as important as causal understanding for the prevention and control of disease. • The earlier you can become aware of the attack the more likely you will be able to intervene and save lives. Triads & Natural History

  27. Reference books • Principles of Epidemiology in Public Health Practice. Third Edition. An Introduction to Applied Epidemiology and Biostatistics. Centers for Disease Control and Prevention (CDC) • Gordis L. Epidemiology. 2009 Triads & Natural History

More Related