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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?
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?
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?
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?
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?
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?
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?
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?
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?
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?
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.