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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?
Which of the following is NOT one of the factors in the epidemiological triad?
What is the term for the interplay between agent, host, and environmental factors in causing a disease?
According to Pettenkoffer, what is the relationship between the agent, host, and environmental factors?
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What is the term for the external factors that contribute to the occurrence of a disease?
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Which of the following is an example of an environmental factor?
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What is the name of the theory that suggests that microbes are the cause of many diseases?
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Who are the scientists who discovered microorganisms in patients' secretions or excretions?
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What is the term for the sequence of events in which a disease progresses from a healthy state to a diseased state?
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What is the term for the range of manifestations of a disease, from mild to severe?
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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.
