Lecture 2: Epidemiology

Question 1

Define epidemiology.

Answer 1

The study of distribution and determinants of health-related states among specified population and the application of that study to the control of health problems

Question 2

What do epidemiologists do?

Answer 2

• Discover the agent, host, and environmental factors that affect health
• Determine the relative importance of causes of illness, disability, and death
• Outbreak investigation
• Identify at-risk segments of the population
• Evaluate the effectiveness of health programs and services in improving population health

Question 3

What are the 2 types of studies?

Answer 3

1. Experimental
2. Observational

Question 4

Define an experimental study.

Answer 4

Intervention in the disease process and study the effect of intervention
- Study therapeutics or vaccines in a population

Question 5

Define an observational study?

Answer 5

No intervention, just observation of diseases process

Question 6

Define cluster.

Answer 6

A group of cases linked by time or place, but with no identified agent or common source

Question 7

Define outbreak.

Answer 7

Sudden increase in number of cases beyond normal (baseline) typically within a small area

Question 8

Define epidemic.

Answer 8

A sudden large increase in number of cases within a specific geographic area

Question 9

Define endemic.

Answer 9

Regularly present within a geographic area

Question 10

Define pandemic.

Answer 10

Epidemic that has spread across international borders and affects large regions and large amounts of people

Question 11

Explain the disease triangle.

Answer 11

Simplified conceptual model that shows the interaction of 3 factors/conditions in causing disease or epidemics/outbreaks
- All 3 conditions must be present and favor disease

Question 12

Explain the role of the pathogen in the disease triangle.

Answer 12

A pathogen must have the ability to establish an infection to cause disease (virulence)

Question 13

Define infective dose.

Answer 13

Number of cells required to successfully infect a host

Question 14

Define virulence factors.

Answer 14

Molecules, proteins, or structures that promote infection

Question 15

What does attenuated mean?

Answer 15

A reduction in virulence to a point where it non longer causes disease

Question 16

What is the role of the host in the disease triangle?

Answer 16

A host must be susceptible
- Must be able to support the infection
- No immunity or insufficient immunity; immunocompromised
- Physiological diseases or disorders
- Trauma
- Behavior

Question 17

What is the role of the environment in the disease triangle?

Answer 17

The surroundings and conditions must favor transmission
- Host availability
- Reservoirs and vectors
- Physical features
- Resources

Question 18

What is the chain of infection?

Answer 18

Set of 6 intertwined links that allow for communicable diseases to spread

Question 19

What is a reservoir (chain of infection)?

Answer 19

Any person, animal, plant, soil, or substance in which an infectious agent normally lives and multiplies

Question 20

How can you intervene with the reservoir?

Answer 20

Eliminate or quarantine the reservoir

Question 21

What is the port of exit (chain of infection)?

Answer 21

How pathogens leave the reservoir/current host

Question 22

How can you intervene with the port of exit?

Answer 22

• Masks
• Sewage systems
• Condoms
• Bandages

Question 23

What are modes of transport/transmission (chain of infection)?

Answer 23

The movement of the pathogen to a new host
- Direct vs indirect

Question 24

Describe direct transmission.

Answer 24

Transmitted directly from reservoir/current host
- Direct contact
- Droplets that don’t stay in the air too long
- Airborne (host still present)

Question 25

Describe indirect transmission.

Answer 25

Current infected host doesn’t have to be present to transmit
- Airborne (after current host is gone)
- Vectors and vehicles

Question 26

How can you intervene with direct transmission?

Answer 26

• Air filters
• Social distancing
• Gloves
• Protective equipment

Question 27

How can you intervene with indirect transmission?

Answer 27

• Pest control
• Filtration
• Ventilation
• Sanitation
• Food safety

Question 28

Describe port of entry/exposure (chain of infection).

Answer 28

How a pathogen enters a host
- Ex. mucous membranes, skin, blood transfusions

Question 29

How can you intervene with port of entry/exposure?

Answer 29

• Masks
• Bandages
• Hand washing/personal hygiene
• Protective equipment

Question 30

How can you intervene with a susceptible host?

Answer 30

• Vaccinations
• Pre-exposure prophylaxis
• Post-exposure prophylaxis
• Exposure risk assessments in CDC website

Question 31

What are the 5 stages of the disease process? Briefly describe each.

Answer 31

1. Incubation period: time between exposure and signs/symptoms
2. Prodromal stage: short period with first signs/symptoms
3. Period of invasion/illness: most evident symptoms
4. Decline: immune system at peak
5. Convalescent period: recovery

Question 32

Define infectious period.

Answer 32

The time when a person can transmit the virus

Question 33

Define carrier.

Answer 33

A colonized or infected host with no clinical illness but can transmit

Question 34

What is the importance of the infectious period?

Answer 34

Important when it comes to contact tracing and quarantine

Question 35

Define basic reproductive number (R₀).

Answer 35

The expected number of secondary cases produced by a single typical infection in a completely susceptible population
- Indicator of the contagiousness of a disease

Question 36

What is the formula for R₀?

Answer 36

transmissibility x average rate of infection x infectious period

Question 37

What is transmissibility?

Answer 37

Probability of infection

Question 38

What does a an R₀ of <1 mean?

Answer 38

That the epidemic will eventually die out