Transmission of infection Flashcards
What is Virulence
The ability of a microbe to cause disease
How are infectious rates of diseases compared
ID50
What does a very low ID50 indicate
Very infectious
What are the possible resrvoirs for disease
Humans
Animals
Environment (soil)
Fomites (on surfaces)
Where do most pathogenic microbes come from
Humans
What is the incubation period for influemza
1-3 days
What is the incubation period for Hep B and C
B - 30 - 180 days
C - 30 - 150 days
What does a long incubation period allow
- longer time periods when the infecting microbe may be spread to others
- greater spread of the disease because of more human contact
What is the podromal phase
Asymptomatic phase (measles, mumps and chickenpox)
What is the difference between colonisation and infection
Colonisation is 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 host in carrying the disease
What is an endogenous reservoir
Caused by members of the normal flora such as periodontal disease/caries
Can also be caused by displacement of normal flora
What is an exogenous reservoir
Diseases caused by microbes from external sources (animals - influenza)
In what ways can microbes escape from the body
Tears
Sneezing]
coughing
blood
respiratory fluids
faeces
urine
What are the 4 hazard groups of human pathogens
Ability to cause infection
Vaccine and treatment available
Severity of the disease
Risk of population spread
What is Ro
the number of cases one case generates on average over the course of its infectious period
What happens when Ro is less than 1
infection will die out in the long run
What factors affect the reproduction number (R0)
Duration of infectivity
Infectiousness
Number of susceptible people
What factors affect aerosol transmission
Size
Viral load and infectivity
pH value
Electrical charge
Air/liquid interfacial properties
What determines the risk factors of fomite mediated transmission
Environmental factors e.g., heat & evaporation while airborne and on fomites
Time between when a surface contaminated and person touching surface
The efficiency of transfer from fomite surfaces to hands & from hands to mucous membranes on the face (nose, mouth, eyes)
The dose of virus needed to cause infection through the mucous membrane route
Why is fomite transmission difficult to prove definitively
Due to the chance of asymptomatic transmission
How can aerosols in dentistry be mitigated
-Use of rubber dam
-High/low volume aspiration
-Surgery ventilation
How many air changes per hour should dental surgeries have
atleast 10
What are examples of portals of entry
Respiratory tract
Gastro-intestinal tract
Open/surgical wounds
Medical devices/Sharps injuries
Sexual contact
What is the portal of entry of influenza
Respiration (aerosols)
Inhalation (all particles)
Direct contact (droplets)
In-direct contact (settled particles – face touching)
Role of conjunctiva uncertain
Who are susceptible hosts
An underdeveloped immune system (neonate)
A declining immune system (elderly)
Disease or drugs that impair host defences
Breaks in the skin
Medical devices
What diseases would enter via these routes:
Respiratory tract
Gastro-intestinal tract
Open/surgical wounds
Medical devices/Sharps injuries
Sexual contact
Resp - influenza
GI - salmonella
Surgical wounds - Staphoreous
Sharps - Hep B
Sexual contact - HIV
