Transmission of Infection Flashcards
what are the basic principles of the chain of infection?
- Infectious agent
- Reservoirs
- Portal of exit
- Means of transmission
- Portal of entry
- Susceptible host
what does virulence mean?
ability of the microbe to cause disease
what does dose mean?
number of microbes entering the body
what factors are included with regards to virulence?
• Exotoxins
○ P.gingivalis (protease)
○ S.aureus (endotoxin & leukocidin)
• Endotoxins
○ Lipopolysaccharide
(P.gingivalis & E.coli)
dont know how to question this / how to understand it but here we are to learn x
infectious dose:
Usually expressed as infectious dose 50 (ID50)
• TB = 1 bacillus
• Syphilis = 57 bacteria (ID50)
• E.coli 0157 = <10 cfu
•Influenza virus = <10 (tissue culture ID50)
name reservoirs where microbes can live
- humans
- animals
- fomites
- environmental
where does most pathogenic microbes that infect humans come from?
other humans
give an example of a human pathogen that comes from animals
anthrax
give an example of a human pathogen that originates in the environment
clostridium tetani spores in soil
what are fomites
Contaminated objects or surfaces
Usually act as a bridge between health care workers and patients
Eg phone, keyboard, medical equipment surfaces, house keeping surfaces
what are the different sources of infection?
> patients in the acute phase of an infection = easily recognised eg influenza, common cold
> patients in the podromal phase of an infection = not easily recognised eg measles, mumps, chickenpox
> healthy carriers of pathogenic organisms = not easily recognised includes convalescent carriers and asymptomatic carriers eg HIV, Hep B and C, herpes viruses
what is the incubation period
the time between contamination and the development of symptoms
varies widely for different infections
what is the problem with longer incubation periods
longer time periods when the infecting microbe may be spread to others
means a greater spread of the disease because of more human contact
define asymptomatic carrier
an infected person with no clinical evidence of disease, though signs and symptoms of the disease may have been evident earlier
why are carriers dangerous in the spread of diseases
they are usually unaware of their infectious state
define colonisation
is the presence of bacteria on a body surface (like on the skin, mouth, intestines etc) with growth and multiplication without causing disease (clinical expression of the infection) in the person
define infection
the invasion of a host organism’s bodily tissues by disease causing organisms
define exogenous
growing or originating outside an organism
caused by microbes from external soruces eg influenza
define endogenous
growing or originating within an organism
caused by members of the normal flora if
- flora becomes ecologically harmful due to population / gene expression shifts eg periodontal disease, dental caries
- they become displaced to another body site or are allowed to invade deeper tissues eg post surgical infections
explain portal of exit
microbes must escape from the source to colonise a new host
what are the different modes of escape (portal of exit)
natural
- coughing
- sneezing
- tears
- urine
artificial
- blood donation
- dental handpiece aerosols
classify pathogens in the 4 hazard groups
- ability to cause infection
- severity of the disease that may result
- risk of population spread
- vaccine and treatment availability
(venn diagram - where these 4 things over lap = extremes = ebola outbreak)
what is R0
the number of cases one case generates on average over the course of its infectious period
explain R0 < 1
infection will die out in the long run
explain R0 > 1
infection will be able to spread in a population
higher R0 number = bigger the risk there is of an infection
what factors affect R0
- duration of infectivity
- infectiousness
- number of susceptible people
what is influenza
infectious agent RNA virus with segmented genome 3 types = A, B, C types A and B cause major outbreaks > X2 surface glycoproteins - hemaglutinin H1-15 - neuraminidase N1-9
what is pathophysiology
the disordered physiological processes associated with disease or injury
what is the pathophysiology of the influenza virus
infection of upper and lower respirator tract
release of cytokines (IF and TNF) = fever, headache, fatigue
explain the infection of influenza
uncomplicated
- fever
- cough
- headaches
- fatigue
complicated
- bacterial pneumonia
- ear and sinus infections
- worsening of chronic medical conditions like asthma and heart disease
what is the incubation period for influenza
2-3 days
infectious as soon as symptoms appear
how is the influenza virus shed
in respiratory tract secretions
what is the infectious period of influenza
3-5 days
children are infectious for longer
not everyone who is infected has obvious symptoms - could be carriers
what is the reservoir for the influenza virus
humans
animals (birds carry the RNA for the disease but pigs jumble the RNA strains together and create new RNA strains)
what is the portal of exit for the influenza virus
large particles
- greater than 10 micrometres
- droplet
- respiratory secretions
- contaminate surfaces
small particles
- smaller than 10 micrometres
- aerosol
- respiratory secretions
- can remain / circulate the air for mins / hours
how long can influenza A and B survive in different surfaces
steel and plastic = 23-48 hours
cloth, paper and tissues = less than 8-12 hours
what is the transmission for influenza
steel to hands over 24 hours
paper tissue to hands for 15mins
survives 5 mins on hands
wha tis the portal of entry for influenza
- respiration (aerosols)
- inhalation (all particles)
- direct contact (droplets)
- in-direct contact (settled particles - face touching)
who are susceptible hosts to influenza
- elderly
- young children
- pregnancy
- chronic medical conditions
> diabetes
> asthma
> heart disease
patients with health conditions are 18 times more likely to die from having the flu
what is the best way to prevent flu
get vaccinated each season
what are the most common strains of influenza circulating
2 circulating A stains and 1 circulating B strain
people who design the vaccination try and predict the strains that are going to be a problem by studying flu in the other hemisphere
