Epidemiology Chapter 1: The Epidemiologic Triad
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Questions and Answers

What is the name of the scientist who, along with Koch, formulated postulates for determining the cause of a disease?

  • Pasteur
  • Pettenkoffer
  • Henle (correct)
  • Asmaa Mohamed Ahmed Soliman
  • Which of the following is NOT one of the factors in the epidemiological triad?

  • Agent Factors
  • Environmental Factors
  • Host Factors
  • Sociological Factors (correct)
  • What is the term for the interplay between agent, host, and environmental factors in causing a disease?

  • Ecological theory
  • Germ theory
  • Multifactorial causation (correct)
  • Supernatural theory
  • According to Pettenkoffer, what is the relationship between the agent, host, and environmental factors?

    <p>They act synergistically</p> Signup and view all the answers

    What is the term for the external factors that contribute to the occurrence of a disease?

    <p>Extrinsic factors</p> Signup and view all the answers

    Which of the following is an example of an environmental factor?

    <p>Poor sanitation</p> Signup and view all the answers

    What is the name of the theory that suggests that microbes are the cause of many diseases?

    <p>Germ theory</p> Signup and view all the answers

    Who are the scientists who discovered microorganisms in patients' secretions or excretions?

    <p>Pasteur, Henle, and Koch</p> Signup and view all the answers

    What is the term for the sequence of events in which a disease progresses from a healthy state to a diseased state?

    <p>Natural history of disease</p> Signup and view all the answers

    What is the term for the range of manifestations of a disease, from mild to severe?

    <p>Spectrum of disease</p> Signup and view all the answers

    Study Notes

    The Epidemiologic Triad

    • The epidemiologic triad consists of three components: an external agent, a susceptible host, and an environment that brings the host and agent together.
    • The environment influences the agent, the host, and the route of transmission of the agent from a source to the host.

    Disease Agents

    • Biological Agents:
      • Viruses
      • Bacteria
      • Fungi
      • Protozoa
      • Helminthes
      • Arthropods
    • Nutrient Agents:
      • Carbohydrates
      • Fats
      • Proteins
      • Minerals
      • Vitamins
      • Water
    • Chemical Agents:
      • Endogenous chemical agents (formed in the body itself)
      • Exogenous Chemical Agents (enter the body from outside)
    • Physical Agents:
      • Heat
      • Cold
      • Humidity
      • Pressure
      • Radiation
      • Electricity
      • Sound (noise)
    • Mechanical Agents:
      • Chronic friction or other mechanical forces which result in injury, sprain, dislocation, or fracture
    • Genetic Disorders:
      • Caused by genetic disorders and lack or under-development of organs

    Host Factors

    • Intrinsic Factors (non-modifiable):
      • Age
      • Race
      • Sex
      • Socioeconomic status
    • Behaviors (modifiable factors):
      • Smoking
      • Drug abuse
      • Lifestyle
      • Sexual practices
      • Contraception
      • Eating habits

    Environmental Factors

    • Physical factors:
      • Geology
      • Climate
    • Biologic factors:
      • Insects that transmit the agent
    • Socioeconomic factors:
      • Crowding
      • Sanitation
      • The availability of health services

    Natural History of Disease

    • Refers to the progress of a disease process in an individual over time, in the absence of intervention.
    • Stages of disease:
      • Pre-pathogenic phase or susceptibility stage
      • Pathogenic phase
        • Incubation period
        • Prodromal stage
        • Stage of overt disease
        • Stage of convalescence

    Spectrum of Disease

    • The idea that an exposure can lead to varying signs, symptoms, and severity of the same disease in the population.
    • The outcome will depend on the interactions of host, agent, and environmental factors.
    • Disease in many forms:
      • Acute
      • Chronic/insidious
      • Carrier

    Iceberg Phenomenon

    • Cases of illness correctly diagnosed by clinicians in the community often represent only the “tip of the iceberg.”
    • Many additional cases may be too early to diagnose or may remain asymptomatic.
    • Examples: Tuberculosis, meningitis, polio, hepatitis A, AIDS.
    • Risk: Persons with in-apparent or undiagnosed infections may be able to transmit infection to others.

    Applications of the Concepts of Natural History and Spectrum of Disease

    • Control measures must not be directed solely for clinically apparent cases.
    • Control measures must be directed toward all infections capable of being transmitted to others; both clinically apparent cases and those with in-apparent or undiagnosed infections.

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    Description

    Learn about the traditional model of infectious disease causation, including the three components of the epidemiologic triad: agent, host, and environment. Understand how the environment influences the agent, host, and route of transmission.

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