Epidemiology

Question 1

Epidemiology

Answer 1

The study of how disease is distributed in populations and the factors that influence or determine this distribution.

Question 2

Direct causal pathway?

Answer 2

Pathogen is necessary and sufficient for disease, cause disease without intermediate steps, all individuals are affected in the same way.

Question 3

Indirect casual pathway?

Answer 3

Pathogen causes disease with intermediate steps and additional factors can affect the development of disease. In humans and animals, this is true in virtually every causal process.

Question 4

What is a cause?

Answer 4

• Something that produces an effect, result, or consequence. If A causes B, then a change in A is associated with a change in B
• In the context of a disease, a causal factor plays an essential role in producing an occurrence of the disease, without which the disease would not have occurred or would have occurred later.

Question 5

Compare association, risk factors, and causes

Answer 5

• Associations go together (smoking and drinking)
• Risk factors increases susceptibility (diet and heart disease)
  Causes: Essential components related
  to progression of disease

Question 6

What is causal framework I: Koch’s?

Answer 6

• Developed early in the era.
• Still have problems: Not all organisms exposed to an agent will acquire the infection or be symptomatic; A single pathogen can cause more than one disease outcome; What about non-infectious diseases?; What about organisms that can’t be cultured?; Experimental models of disease are imperferct.

Question 7

What is causal framework II: 1964?

Answer 7

9 Criteria:
1. Temporality: Exposure to the causal agent must have occurred before the disease developed. (REMEMBER!)
2. Strength of Association
3. Dose-response
4. Experiment
5. Consistency/Replication
6. Biological Plausibility
7. Alternate Explanations
8. Specificity
9. Coherence

Question 8

What is causal framework III: 1986?

Answer 8

1. Temporality
2. Biological plausibility
3. Consistency
4. Lack of confounding

Question 9

List risk factor epidemiology

Answer 9

– Predisposing factors (distant; social determinants)
– Enabling factors (intermediate; risk factors)
– Precipitating factors (proximate; direct or final cause)

Question 10

What is causal framework IV: Agent-Host-Enviornment?

Answer 10

• Agent: bad tires, no airbags
• Host: poor health, inexperience drivers
• Environment: road, time of dat, intersections
  (Example only)

Question 11

What’s causal Framework V: Causal Pies?

Answer 11

• Necessary causes must precede disease, but their presence does not guarantee disease. This cause is present in every “pie”.
• Sufficient causes: if you have A, you will ALWAYS have B. In other words, if something is a sufficient cause, then every time it happens the outcome will follow. The outcome always follows the cause. However, the outcome may occur without the cause.
• If A is neither necessary nor sufficient for B then sometimes when A happens B will happen. B can also happen without A. The cause sometimes leads to the outcome, and sometimes the outcome can happen without the cause.
• If A is both sufficient and necessary for B, B will never happen without A. Furthermore, B will ALWAYS happen after A. The cause always leads to the outcome, and the outcome never happens without the cause.

Question 12

Define and understand what constitutes an “outbreak”

Answer 12

Outbreaks/Epidemics occur when number of disease cases exceed what is normally expected.
Versus endemic – typical occurrence (incidence) in a geographic area
Baseline of disease occurence constitutes an outbreak.

Question 13

Define and understand what “endemic” vs. “epidemic” means how that applies to outbreaks

Answer 13

• Epidemic – cases in excess of expected in a geographic area
• Endemic – Typical occurrence (incidence) in a geographic area

Question 14

Understand the components of a “case-definition”

Answer 14

• Clinical Signs
• Suspect case: An animal having clinical signs and epidemiological information consistent with dz.
• Presumptive positive case: A suspect that has positive screening laboratory results for dz.
• Confirmed positive case: An animal from which virus has been isolated and identified at a laboratory.

Question 15

Understand the difference between “point-source” and “propagated” outbreak transmission

Answer 15

Point source: oil spill, tanzanite spill sacramento, “sushi”
Propagated outbreak: HPAI, ebola

Incubation period = the period between the infection of an individual by a pathogen and the manifestation of the illness or disease it causes

Question 16

Understand and define the concept of “attributable proportions” and “relative-risk”

Answer 16

Affected proportion 1: diseased / total exposed
Affected proportion 2: diseased / total not exposed
Attributable proportion = AP1 - AP2
Relative risk = AP1/AP2
RR = 1 = no assocition
RR > 1 = positive association, possible causal.
RR < 1 = negative association, possibly protective.

Question 17

How does a disease introduce to an individual or population?

Answer 17

● Contamination: Presence of disease-causing agent on exterior surface of body or on bandages, water, milk, food
● Pollution: Presence of offensive but not necessarily infectious matter in the environment
● Exposure: Contact or close proximity to an agent
● Infection: The entry and development or multiplication of an infectious agent in the body of animals.

Question 18

Timeline of a disease?

Answer 18

• Incubation period: the interval between effective exposure to an agent (usually an infectious disease agent) and the onset of related disease
• Induction period: the time from exposure to the (often oncogenic) chemical to the detection of related disease
• Latent or prepatent period: the interval between the time of infection and when the organism begins to be shed (often used with viruses, bacteria, and parasites)

Question 19

Understand the mechanisms underlying of introduction of a disease into an individual and population

Answer 19

• Timeline: incubation, induction, and latent/prepatent period.
• Diseases: reservoir or ecological or evolutionary host; carrier.
  = Healthy carrier (asymptomatic throughout time)
  = Incubatory carrier (carry pathogen but not symptomatic)
  = Convalescent carrier (Typhoid Mary - subclinical, recovered from dz but still transmit pathogen)
• Transmission: Direct; indirect (vector, environmental contamination, biologicals, fomites); vertical transmission (from mother to offspring via placenta).

Question 20

Understand the key principles of the concept of herd immunity either naturally acquired or through medical countermeasures (e.g., vaccines)

Answer 20

• Occurs when a large portion of members are immune, thus lessening the likelihood of a diseased individual coming into contact with a susceptible
• Differentiate from herd resistance (more inclusive) that may be circumstantial due to quarantine of potential additions or the operation of a closed herd