Transmission of Infection Flashcards
6 steps in chain of infection
- infectious agent
- reservoir
- portal of exit
- means of transmission
- portal of entry
- susceptible host
virulence is
the ability of the microbe to cause damage
dose is
the number of microbe entering the body
what are 2 virulence factors?
- endotoxins
- exotoxins
examples of exotoxins are…
P. gingivalis (protease)
S. aureus enterotoxin (food poisoning??)
leukocidin (WBC)
endotoxin examples are…
Lipopolysaccharide
P. gingivalis (periodontal disease) & E. coli
what are exotoxins and how are they released?
gram positive
released by an active process
what are endotoxins and how are they released?
generally gram negative
released from cell walls
what is the infectious dose 50 (ID50)?
dose of an infectious organism required to produce infection in 50% of the experimental subjects
where do most pathogenic microbes that infect humans come from?
other humans
how recognisable are healthy carriers of pathogenic organisms?
not easily recognised
includes convalescent carries and asymptomatic carriers
e.g. HIV, hep B and C, herpes
how recognisable are patients in podromal phase of infection?
not easily recognised
e.g measles, mumps, chickenpox
how recognisable are patients in the acute phase of infection?
easily recognised
e.g. influenza and common cold
what term is used for human pathogens that come from animals?
zoonoses
e.g. anthrax
example of human pathogen that originates from the environment
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
4 sources of human pathogens
- humans
- animals
- environment
- fomites
what are fomites?
contaminated objects or surfaces
what do fomites do?
usually act as a bridge between healthcare worker and patient
e.g. hand contact, phone on clinic
what is done to try and reduce fomite contamination?
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
what do long incubation periods permit
longer time periods when the infecting microbe may be spread to others
greater spread of the disease because of more human contact
asymptomatic carrier
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
why is it important to have standard infection control procedures?
asymptomatic carriers
- need to have equal risk precautions
- Not logical to discriminate against any patient
what is a key factor to remember regarding carriers?
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
colonisation
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
endogenous reservoir
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
exogenous reservoir
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
purpose of poral of exit
microbes escape the source to colonise new host
what are the 2 types of mode of escape?
NATURAL (e.g. coughing or sneezing)
ARTIFICIAL (e.g. blood donation or dental handpiece aerosols)
how are biological agents classified?
according to the risks to human health, animals, plants and the environment
COSHH
what are the 4 bases COSHH uses to classiffy human pathogens?
- ability to cause infection (virulence)
- severity of the disease it may result in
- vaccine and treatment availability
- risk of population spread
R0
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”.
when R0 < 1
infection will die out in the long run
when R0 > 1
infection will be able to spread in a population
- greater risk of widespread infection and epidemic higher the R0
when the 4 factors for COSHH overlap can result in….
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
3 factors effecting R0
- Duration of infectivity
- Infectiousness
- Number of susceptible people
what type of virus is influenza?
RNA virus with segmented genome
how many types of influenza virus is there?
3
A, B, C
what types of influenza virus cause the major outbreaks?
A and B
what are the 2 glycoprotiens on influenza and what are their roles?
Hemagglutinin H1-15
- Classified by
Neuraminidase N1-9
- Used to break out of cells
what is the 2 pathophysiology routes of influenza?
Infection of Upper Respiratory Tract & Lower Respiratory Tract cells (RTI symptoms)
Release of cytokines (Interferon (IF) & TNF) = fever, headache & fatigue
what symptoms does mild uncomplicated influenza have?
fever, cough, headaches, fatigue etx
what symptoms does severe complicated influenxa have?
Bacterial pneumonia, ear & sinus infections
Worsening of chronic medical conditions (asthma, heart disease)
flu virus shedding
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
how long is someone infectious with influenza?
3-5 days
children longer
what are influenza reservoirs?
humans animals (SE Asia - close human and bird proximity means melting point for viral re-assembly)
2 classes of respiratory secretions
- droplets
- aerosols
droplets
large particles from respiratory tract
approx >10nm
aerols
small particles from respiratory tract
approx <10nm
travel of droplet secretions
land on surface
picked up by hands
travel of aerosol secretion
carried in air circulation in surgery
- time carried depends on ventilation
how long will influenza A and B survive on steel and plastic?
24-48 hours
how long will influenza A and B survive on cloth, paper and tissues?
<8-12 hours
how can transmission of influenza occur after respiratory exit?
- Steel to hands over 24 hours
- Paper tissue to hands for 15 mins
- Virus survives approx 5 mins on hands
what is a major common vector in respiratory tract viruses?
hands
portal of exit for influenza virus
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
susceptible hosts risk groups for influenza
Elderly, young children, pregnant & chronic medical conditions (diabetes, asthma, heart disease)
Patients with health conditions are x18 times more likely to die from flu
why is childhood flu vaccine for 2-5 year olds good?
Good as children carry influenza virus and are more infectious for longer
Can spread to at risk groups easily through nursery schools and grandparents
why should healthcare workers get the flu vaccine?
- 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
