Lecture 7.1: Control of Infectious Diseases Flashcards

1
Q

Potential of an infectious agent to spread in a
population is dependent on 4 factors, name them

A
  • Probability of transmission in a contact between an.
    infected individual and a susceptible one
  • Frequency of contacts in the population - contact
    patterns in a society
  • Duration of infectiousness
  • Proportion of the population/contacts that are already
    immune, not susceptible
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2
Q

What does a R0<1 mean?

A

The disease will disappear

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3
Q

What is the Basic Reproductive Rate (R0)?

A

Average number of individuals directly infected by an infectious case (secondary cases) during his or her entire infectious period, when she or he enters a totally susceptible population

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4
Q

What does a R0=1 mean?

A

The disease will become endemic

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5
Q

What does a R0> 1 mean?

A

There will be an epidemic

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6
Q

What is an Epidemic?

A

It is the rapid spread of disease to a large number of hosts in a given population within a short period of time

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7
Q

What does it mean when a disease is Endemic?

A

Regularly occurring within an area or community

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8
Q

R0 is Affected By…? (3)

A
  • The frequency of contacts in the host population
  • The probability of infection being transmitted during
    contact
  • The duration of infectiousness
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9
Q

Basic formula for the actual value of R0?

A

R0= β * κ * D

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10
Q

What does β stand for in R0= β * κ * D? What can affect β?

A
  • Risk of transmission per contact (i.e. attack rate)
  • Condoms, face masks, hand washing –> β ↓
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11
Q

What does κ stand for in R0= β * κ * D? What can affect κ?

A
  • Average number of contacts per time unit
  • Isolation, closing schools, public campaigns –> κ ↓
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12
Q

What does D stand for in R0= β * κ * D? What can affect D?

A
  • Duration of infectiousness measured by the same time
    units as κ
  • Specific for an infectious disease
  • Early diagnosis and treatment, screening, contact tracing
    –> D ↓
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13
Q

What is the Effective Reproductive Number (R)?

A

It is the expected number of new infections caused by an infectious individual in a population where some individuals may no longer be susceptible

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14
Q

What is Immunisation?

A
  • Immunisation is the process whereby a person is
    made immune or resistant to an infectious disease,
    typically by the administration of a vaccine
  • Vaccines stimulate the body’s own immune system to
    protect the person against subsequent infection or
    disease
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15
Q

What is Herd Immunity?

A
  • Level of immunity in a population which prevents.
    epidemics even if some transmission may still occur
  • Presence of immune individuals protects those who
    are not themselves immune
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16
Q

What is the Herd Immunity Threshold?

A

Minimum proportion (p) of population that needs to be immunised in order to obtain herd immunity

17
Q

How to calculate the Herd Immunity Threshold?

A

p = 1 - 1/R0

18
Q

What is an Outbreak?

A

Occurrence of more cases of disease than expected in a
given area, among a specific group of people, over a particular period of time

19
Q

Why Investigate Outbreaks? (8)

A
  • Stop the outbreak
  • Find and neutralise the source (cause)
  • Prevent additional cases
  • Prevent future outbreaks
  • Improve surveillance and outbreak detection
  • Improve our knowledge
  • Keep the public’s confidence
  • Training
20
Q

Steps Involved in Outbreak Investigation (9)

A
  • Confirm outbreak and diagnosis
  • Define a case
  • Identify cases & obtain information
  • Describe data collected and analyse
  • Develop hypothesis
  • Test hypothesis: analytical studies
  • Special studies
  • Communicate results
  • Implement control measure
21
Q

Multi Locus Sequence Typing (MLST)

A

Characterisation of bacterial isolates based on the combination of alleles at multiple loci (gene fragments)

22
Q

Whole Genome Sequencing (WGS)

A
  • Characterisation of isolates based on unique whole
    genome sequences
  • There is some debate about how to interpret WGS in
    their entirety
23
Q

Examples of Epidemic Curves: Common Point Source

A
  • Commonly associated with foodborne illness, where
    many people are exposed for a short period of time
  • Note lack of person-to-person transmission
24
Q

Examples of Epidemic Curves: Common Persistent Source

A

Outbreak due to exposure of persons to a noxious influence that is common to the individuals in the group

25
Q

Examples of Epidemic Curves: Propagated Source

A

An epidemic that arises when a primary case introduces an infectious agent to a population and subsequent host-to-host transmission results in ‘waves’ of cases

26
Q

Lab confirmation of Campylobacter takes….hours?

A

96