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BDS2 BAMS > Transmission of Infection > Flashcards

Transmission of Infection Flashcards

1
Q

6 steps in chain of infection

A
  • infectious agent
  • reservoir
  • portal of exit
  • means of transmission
  • portal of entry
  • susceptible host
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2
Q

virulence is

A

the ability of the microbe to cause damage

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3
Q

dose is

A

the number of microbe entering the body

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4
Q

what are 2 virulence factors?

A
  • endotoxins

- exotoxins

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5
Q

examples of exotoxins are…

A

P. gingivalis (protease)

S. aureus enterotoxin (food poisoning??)

leukocidin (WBC)

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6
Q

endotoxin examples are…

A

Lipopolysaccharide

P. gingivalis (periodontal disease) & E. coli

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7
Q

what are exotoxins and how are they released?

A

gram positive

released by an active process

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8
Q

what are endotoxins and how are they released?

A

generally gram negative

released from cell walls

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9
Q

what is the infectious dose 50 (ID50)?

A

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

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10
Q

where do most pathogenic microbes that infect humans come from?

A

other humans

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11
Q

how recognisable are healthy carriers of pathogenic organisms?

A

not easily recognised

includes convalescent carries and asymptomatic carriers
e.g. HIV, hep B and C, herpes

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12
Q

how recognisable are patients in podromal phase of infection?

A

not easily recognised

e.g measles, mumps, chickenpox

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13
Q

how recognisable are patients in the acute phase of infection?

A

easily recognised

e.g. influenza and common cold

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14
Q

what term is used for human pathogens that come from animals?

A

zoonoses

e.g. anthrax

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15
Q

example of human pathogen that originates from the environment

A

Clostridium tetani spores in soil
- terminal enlargements are the infectious parts

dental example – collision with tarmac, clean out foreign toxic material and top up tetanus jab

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16
Q

4 sources of human pathogens

A
  • humans
  • animals
  • environment
  • fomites
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17
Q

what are fomites?

A

contaminated objects or surfaces

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18
Q

what do fomites do?

A

usually act as a bridge between healthcare worker and patient

e.g. hand contact, phone on clinic

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19
Q

what is done to try and reduce fomite contamination?

A

different strategies and cleaning orders devised based on likelihood to spread to your hands

  • medical equipment surfaces - need cleaned between each patient use
  • household surfaces e.g. floors, walls, ceilings - less likely to transmit; clean daily
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20
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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21
Q

asymptomatic carrier

A

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

  • May not know they are a carrier
  • Fail to disclose their risk factors
  • Unaware
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22
Q

why is it important to have standard infection control procedures?

A

asymptomatic carriers

  • need to have equal risk precautions
  • Not logical to discriminate against any patient
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23
Q

what is a key factor to remember regarding carriers?

A

most are unaware they are carriers
- them and people around them ignorant to their infectious state

key to spread of disease
e.g. blood bourne viruses like HIV

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24
Q

colonisation

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
- E.g. nose is a carriage site for S.aureus

Important clinically as may not need to treat if colonisation
- Can grow from swab

25
Q

endogenous 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

26
Q

exogenous reservoir

A

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)
Endo flora in wrong location e.g. in dental pulp
- Change in flora inhabiting it
- Sugar splitting flora to protein splitting flora
Acquired from somewhere else

OR

diseases caused by microbes from external sources e.g. inflluenza

27
Q

purpose of poral of exit

A

microbes escape the source to colonise new host

28
Q

what are the 2 types of mode of escape?

A

NATURAL (e.g. coughing or sneezing)

ARTIFICIAL (e.g. blood donation or dental handpiece aerosols)

29
Q

how are biological agents classified?

A

according to the risks to human health, animals, plants and the environment

COSHH

30
Q

what are the 4 bases COSHH uses to classiffy human pathogens?

A
  • ability to cause infection (virulence)
  • severity of the disease it may result in
  • vaccine and treatment availability
  • risk of population spread
31
Q

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”.

32
Q

when R0 < 1

A

infection will die out in the long run

33
Q

when R0 > 1

A

infection will be able to spread in a population

- greater risk of widespread infection and epidemic higher the R0

34
Q

when the 4 factors for COSHH overlap can result in….

A

extreme outbreaks and epidemics

single factors alone mean likely to survive

  • ability to cause infection (virulence)
  • severity of the disease it may result in
  • vaccine and treatment availability
  • risk of population spread
35
Q

3 factors effecting R0

A
  • Duration of infectivity
  • Infectiousness
  • Number of susceptible people
36
Q

what type of virus is influenza?

A

RNA virus with segmented genome

37
Q

how many types of influenza virus is there?

A

3

A, B, C

38
Q

what types of influenza virus cause the major outbreaks?

A

A and B

39
Q

what are the 2 glycoprotiens on influenza and what are their roles?

A

Hemagglutinin H1-15
- Classified by

Neuraminidase N1-9
- Used to break out of cells

40
Q

what is the 2 pathophysiology routes of influenza?

A

Infection of Upper Respiratory Tract & Lower Respiratory Tract cells (RTI symptoms)

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

41
Q

what symptoms does mild uncomplicated influenza have?

A

fever, cough, headaches, fatigue etx

42
Q

what symptoms does severe complicated influenxa have?

A

Bacterial pneumonia, ear & sinus infections

Worsening of chronic medical conditions (asthma, heart disease)

43
Q

flu virus shedding

A

Incubation period 2-3 days

Infectious once symptoms appear
- Not everyone who gets infected shows symptoms but still act as a vector

Virus shed in upper respiratory tract secretions

Infectious for 3-5 days
- Children infectious for longer

44
Q

how long is someone infectious with influenza?

A

3-5 days

children longer

45
Q

what are influenza reservoirs?

A 
humans
animals  (SE Asia - close human and bird proximity means melting point for viral re-assembly)
46
Q

2 classes of respiratory secretions

A
  • droplets

- aerosols

47
Q

droplets

A

large particles from respiratory tract

approx >10nm

48
Q

aerols

A

small particles from respiratory tract

approx <10nm

49
Q

travel of droplet secretions

A

land on surface

picked up by hands

50
Q

travel of aerosol secretion

A

carried in air circulation in surgery

- time carried depends on ventilation

51
Q

how long will influenza A and B survive on steel and plastic?

A

24-48 hours

52
Q

how long will influenza A and B survive on cloth, paper and tissues?

A

<8-12 hours

53
Q

how can transmission of influenza occur after respiratory exit?

A
  • Steel to hands over 24 hours
  • Paper tissue to hands for 15 mins
  • Virus survives approx 5 mins on hands
54
Q

what is a major common vector in respiratory tract viruses?

A

hands

55
Q

portal of exit for influenza virus

A

droplets/aerosols picked up by

  • Respiration (aerosols)
  • Inhalation (all particles)
  • Direct contact (droplets)
  • In-direct contact (settled particles – face touching)
  • Role of conjunctiva uncertain

Need to aware of how often touch face/head with hands after and during examination – often; bad habit

56
Q

susceptible hosts risk groups for influenza

A

Elderly, young children, pregnant & chronic medical conditions (diabetes, asthma, heart disease)

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

57
Q

why is childhood flu vaccine for 2-5 year olds good?

A

Good as children carry influenza virus and are more infectious for longer

Can spread to at risk groups easily through nursery schools and grandparents

58
Q

why should healthcare workers get the flu vaccine?

A
  • Best way to help protect against flu that year
  • Reduces 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
  • Free

Have a moral/ethical reason to get it

BDS2 BAMS (54 decks)

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