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Epidemiology > Lecture 20 Epi of Infectious Diseases > Flashcards

Lecture 20 Epi of Infectious Diseases Flashcards

1
Q

Modes of Transmission
Contact

A
  1. Direct Contact (touching, kissing, sex)
  2. Indirect contact (intermediate object, fomites)
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2
Q

MOT: Respiratory Droplets

A

Secretion particles, coughing, sneezing.

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3
Q

MOT: Airborne

A

Particles that are less than 5 microns: droplet nuclei, dust

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4
Q

MOT: Vehicle-Borne

A

Ingestion of contaminated food or water, instrumentation, infusion/injection

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5
Q

MOT: Vertical Transmission

A

In utero, birth, breastmilk

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5
Q

MOT: Vector-born

A

Mechanical, biologic

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6
Q

Airborne Transmission

A

Suspended microorganisms are inhaled by a susceptible host and cause infection. Think about the stadium crisis. Air flow in the stadium carried the microorganisms to all parts of the stadium and people got sick.
1. Depends on temperature and humidity
2. Droplet nuclei less than 5microns
3. Microorganisms can travel considerable distances.

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7
Q

Droplet Transmission

A

Droplets are propelled from an infectious host onto an other susceptible host to cause infection. Propelled via talking, sneezing, etc and they fall to the floor.
1. Larger than 5 microns
2. Do not remain in air for long and require proximity. (6-10 microns can be suspended briefly
3. Microorganisms travel 3-6 feet

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8
Q

Epidemiologic Triad

A

A way to describe the interactive mechanism between host, vector, agent, and environment.
It’s not the most optimal way to describe the how disease spreads

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9
Q
A
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10
Q

Chain Model of Infectious Disease
What is the first circle?

A
  1. Susceptible host
    Someone with a compromised immune system.
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11
Q

Chain Model of Infectious Disease
What is the second circle?

A
  1. Causative Agent
    Also known as the pathogen
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12
Q

Chain Model of Infectious Disease
What is the third circle?

A
  1. Reservoir or Host
    The thing in which the pathogen is already living in.
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13
Q

Chain Model of Infectious Disease
What is the fourth circle?

A
  1. Portal of exit
    The way the pathogen leaves the reservoir/host
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14
Q

Chain Model of Infectious Disease
What is the fifth circle?

A
  1. Mode of Transmission
    The way the pathogen travels, can be 6 different ways
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15
Q

Chain Model of Infectious Disease
What is the sixth circle?

A
  1. Portal of entry
    How the pathogen enters the susceptible host
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16
Q

Chain Model of Infectious Disease
What is the seventh circle?

A
  1. Back to susceptible host
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17
Q

Infectivity

A

The ability of an infectious agent to establish infection in a susceptible host. Infectivity is high if it takes a minimal amount of exposure to the infectious particles.
Measured in:
Number of infectious particles
Secondary attack rate

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18
Q

Pathogenicity

A

Proportion of infections that result in clinically apparent infection or disease. Person has symptoms

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19
Q

Virulence

A

Proportion of clinically apparent cases that result in significant clinical manifestations
Measured by case fatality

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20
Q

Natural History of Disease (Pathogen Perspective)

A
  1. Latent Period
  2. Infectious Period
  3. Non-infectious Period
21
Q

Natural History of Disease (Host Perspective)

A
  1. Incubation Period
  2. Symptomatic Period
  3. Non-diseased Period
22
Q

What is the latent period?

A

Period of time after infection where the pathogen is not yet infectious

23
Q

What is the infectious period?

A

Period of time where the pathogen is infectious.

24
Q

What is the non-infectious period?

A

Pathogen is no longer infectious due to
1. Immunity
2. Death (pathogen can still cause damage)
3. Recovery

25
Q

What is the incubation period?

A

Period of time after infection. You can either have symptoms or no symptoms by this point.

26
Q

What is the symptomatic period?

A

When the infected person develops apparent symptoms.

27
Q

What is the non-diseased period?

A
  1. Become immune
  2. Become a carrier
  3. Die
  4. Recovered
28
Q

Influenza

A

Individuals are contagious before they develop symptoms.

29
Q

Smallpox

A

People are symptomatic before they become infectious.

30
Q

Sars 2003

A

Individuals are contagious only when they experience symptoms.

31
Q

Sars-Cov-2

A

Individuals are contagious before they develop symptoms.
Infectious before symptomatic

32
Q

What is the SIR Model?

A

Susceptible
Infected
Recovered

33
Q

Susceptible

A

People who are at risk for developing the disease

34
Q

Infected

A

People are infected with disease/illness

35
Q

Recovered

A

Those who have recovered from the disease and are no longer susceptible.

36
Q

Epidemic Theory

A

Once there are no longer any susceptible people the outbreak will die out. Exceptions are the SIS model which is susceptible, infected, susceptible again.

37
Q

Basic Reproductive Number (R0)

A

The expected number of new infectious hosts that a primary infectious host will produce during their infectious period in a large, susceptible population.
Does not include new cases produced by secondary cases

38
Q

Why is R0 not realistic?

A

Very rarely do we have completely susceptible populations so we don’t measure RO usually. (Sars covid-2 was exception; everyone was susceptible)

39
Q

Effective Reproductive Number

A

Used in populations that are not completely susceptible (reality)
RO * x (the fraction of the population that is susceptible)
shelter in place, vaccinations can help change x
RO does not change it stays the same
R can change over time depending on what humans and pathogen is doing

40
Q

Herd Immunity

A

there is protection offered by presence and proximity of immune people even if the person themselves is not immune because the other immune people won’t spread the disease.

41
Q

herd immunity threshold

A

minimum proportion of a population that must be immune for elimination of infection
If R0 is high, the higher the more people that need to be immune to achieve an R < 1.

42
Q

R > 1

A

If R is > 1 that means one infectious host is producing on average more than one infected people. This is a recipe for outbreak.

43
Q

R < 1

A

If R < 1 that means one infectious host is producing on average less than one infected person. Outbreak will die out.

44
Q

R = 1

A

Outbreak is in equilibrium. One infectious host produces one infected person.

45
Q

The concept of flattening the curve

A

If R is much greater than 1 then it produces a high epidemic curve. The x-axis represents infected people on a

46
Q

Which of the following about effective reproductive rate (R) in infectious disease epidemiology is FALSE?

A
47
Q

Which of the following about effective reproductive rate (R) in infectious disease epidemiology is FALSE?

A

Choice 1 of 5:Disease with a higher R could be a more infectious disease.

Choice 2 of 5:Increasing the proportion of the population that is susceptible will increase the effective reproductive rate.

Choice 3 of 5:Changes in R can reflect the success of our control efforts.

Choice 4 of 5:An outbreak with R > 1 will continue to spread while R < 1 will eventually die out.

Choice 5 of 5:
R0 is equal to the effective reproductive rate scaled by the proportion of the population that is susceptible.

48
Q

Which of the following statements around measles describes pathogenicity?

A

Individuals who contract measles often have a prominent rash 10-14 days after exposure.

49
Q
A

Epidemiology (13 decks)

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