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BDS2 BAMS lectures > Transmission of infection > Flashcards

Transmission of infection Flashcards

1
Q

What is virulence

A

the ability of the microbe to cause disease

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2
Q

What is dose

A

the number of microbes entering the body

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3
Q

Examples of virulence factors

A

Exotoxins
P. gingivalis (protease)
S. aureus (enterotoxin and leukocidin)

Endotoxins 
Lipopolysaccharide
(P. gingivalis and E.coli)
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4
Q

What is ID50

A

the dose of an infectious organism required to produce infection in 50% of the experiment subjects

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5
Q

What is the chain of infection

A 
Infectious agent
Reservoirs
Portal of exit
Means of transmission
Portal of entry
Susceptible host
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6
Q

Four main reservoirs?

A

humans, animals (zoonoses), environmental and fomites

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7
Q

What are fomites

A

contaminated objects or surfaces

  • medical equipment surfaces
  • house keeping surfaces
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8
Q

What is the incubation period

A

the time between contamination and the development of symptoms

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9
Q

What do long incubation periods permit?

A
  • longer time periods when the infecting microbe may be spread to others
  • greater spread of the disease because of more human contact
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10
Q

What is an asymptomiatic carrier

A

an infected person with no clinical evidence of disease though signs and symptoms of the disease may have been evident earlier

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11
Q

What are carriers

A

are usually not aware of their infectious state

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12
Q

What is the difference between colonisation and infection

A

the presence of micro-organism (s) in or on a host, with growth and multiplication, but without any overt clinical expression (infection) at the time the micro-organism is isolated

the difference is important

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13
Q

Endogenous or exogenous reservoir?

A

Caused by members of the normal flora if:
Flora becomes ecologically harmful due to population/gene expression shifts e.g. periodontal disease and dental caries

Caused by members of the normal flora if:
they become displaced to another body
site or are allowed to invade deeper tissues
(e.g. post-surgical infections)

Diseases caused by microbes from
external sources, e.g. influenza

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14
Q

How does a microbe escape?

A

Microbes must ESCAPE from the source to
colonise a new host
• Mechanisms of escape vary depending upon the source.

• Mode of escape may be:
• NATURAL (e.g. coughing or sneezing)
• ARTIFICIAL (e.g. blood donation or dental
handpiece aerosols)

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15
Q

Examples of how microbes escape the body

A 
tears
nasal secretions
saliva
blood
respiratory fluids and sputum
blood and tissue fluids exiting through small breaks in the skin or through injuries
contact with the skin
breast milk
faeces
intestinal fluids
semen
vaginal secretions
urine
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16
Q

How does COSHH classify human pathogens into 4 hazard groups

A

Based on:

  • ability to cause infection
  • vaccine and treatment avaliability
  • severity of the disease that may result
  • vaccine and treatment avaliability
  • risk of population spread
17
Q

What is R0

A

the number of cases one case generates on average over the course of its infectious period

In an otherwise uninfected population, the expected number of secondary cases produced by a typical infected individual early in an epidemic

18
Q

What happens when R0 is less than 1

A

the infection will die out

19
Q

What happens when R0 is more than 1

A

infection is able to spread in a population

20
Q

What factors affect R0

A
  • duration of infectivity
  • infectiousness
  • number of susceptible people
21
Q

How many types of influenza are there?

A

A,B and C

22
Q

What are the surface proteins on influenza

A

Hemaglutinin H1-15

Neuraminidase N1-9

23
Q

What is the pathophysiology of influenza

A

Infection of URT & LRT cells = RTI symptoms

Release of cytokines (IF & TNF) = fever, headache & fatigue

Incubation period 2-3 days
Infectious once symptoms appear
Virus shed in upper respiratory tract secretions
Infectious for 3-5 days
Children infectious for longer
24
Q

What did a study about respiratory infections in GDPs as opposed to the rest of the population find?

A

GDPs have significantly raised antibody titres compared to controls for Flu A, B and RSV

25
Q

What size are influenza particles?

A

Both small and large
small (approx <10um) = aerosol
large (approx >10um) = droplet

26
Q

how long does influenza survive on steel and plastic?

A

24-48 hours

27
Q

how long does influenza survive on cloth, paper and tissues?

A

under 8-12 hours

28
Q

What is a particularly common transmission portal of entry for influenza?

A

hands

29
Q

How can viruses enter?

A

Virus entry

  • respiration (aerosols)
  • inhalation (all particles)
  • direct contact (droplets)

Indirect contact
- role of conjunctiva uncertain

30
Q

Who are the particular risk groups (susceptible hosts)

A

Elderly, young children, pregnancy and chronic medical conditions

unvaccinated

Patients with health conditions are x18 times more likely to die from flu

31
Q

Why should dentists have flu vaccine

A
  • best way to help protect against flu this year
  • reduces the risk of spreading flu to your patients, family and colleagues
  • infected dentists can spread flu even if they have very mild symptoms or have no symptoms at all
32
Q

define outbreak

A

the occurrence of more cases of a disease than would normally be expected in a specific place or group of people over a given period of time

33
Q

define point source outbreak

A

persons are exposed to the same source over a brief time, such as through a single meal or at an event. The number of cases rises rapidly to a peak and falls gradually. Most cases occur within one incubation period

34
Q

define colonisation

A

indicates the presence of an organism without signs or symptoms of illness. It can occur in the nares, oral cavity, throat and trachea or in an open wound such as a pressure sore. The patient does not have symptoms when colonised. Infection indicates the presence of an organism with clinical signs and symptoms of illness

35
Q

define colifoms

A

gram negative rods commonly used as a marker of faecal contamination of water and foods. They are found in the aquatic environment, soil, vegetation and are commonly found in large numbers in the faeces of animals. Eg C.coli and S. marcescens

36
Q

What are serratia marcescens

A

serratia species are opportunistic gram-negative bacteria part of the large family enterobacteriaceae. Serratia are widespread in the environment and can be found in the GI tract

BDS2 BAMS lectures (9 decks)

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