Transmission of infection Flashcards
ILO 1.14a: have knowledge of the causes of infection, mechanisms and routes of spread of infection and principles of treatment (25 cards)
what is in the chain of infection?
6
- susceptible host
- infectious agent
- reservoirs
- portal of exit
- means of transmission
- portal of entry
give examples of reservoirs
6
- humans
- equipment/formites
- the environment
- food
- water
- animals
give examples of portal of exit
4
- blood and other bodily fluids
- skin scales
- coughing and sneezing
- droplets and aerosols
give examples of mode of transmission
6
- direct physical contact
- contaminated objects
- air via coughing
- contact with blood or body fluids
- contaminated food/water ingestion
- insects or animals
give examples of portal of entry
6
- open/surgical wounds
- broken skin
- eyes or mouth
- respiratory tract
- intestinal tract
- tubes inserted into the body
give examples of susceptible hosts
5
- under-developed immune system (infants)
- weakened immune system (elderly, cancer pts)
- breaks in skin
- tubes inserted into the body
- drugs/disease that lower defence against infections
give examples of infectious agents
3
- bacteria
- viruses
- fungi
what is virulence?
the ability of a microbe to cause disease
what is infectious dose?
the number of microbes entering the body
* usually expressed as ID50 which is the international reference standard to compare infectivity of microbes across different species and under different conditions
what are the two virulence factors?
exotoxins
endotoxins
what are exotoxins?
- produced by gram positive and negative bacteria
- secreted into the external environment
- p. gingivalis (protease)
- s. aureus (enterotoxin and leukocidin)
what are endotoxins?
- produced by gram negative bacteria
- released from cell walls
- p. gingivalis and e. coli (lipopolysaccharides)
what is the incubation period?
the time between contamination and the development of symptoms
what do longer incubation times permit?
2
- longer time periods when the infecting microbe may be spreading to others
- greater spread of the disease because of more human contact
what is an asymptomatic carrier?
an infected person with no clinical evidence of disease
what is an endogenous reservoir?
2
caused by members of the normal flora if:
* the flora becomes ecologially harmful due to population/gene expression shifts e.g. periodontal disease or caries
* they become displaced to another body site or are allowed to invade deeper tissues e.g. post-surgical infections
what is an exogenous reservoir?
diseases caused by microbes from external sources e.g. influenza
what are the four hazard groups that COSHH classifies human pathogens?
- ability to cause disease
- severity of the disease that may result
- vaccine and treatment availability
- risk of population spread
what is R0 value? what does it mean if it is more or less than 1?
3
- the number of cases one case generates on average over the course of its infectious period
- when R0>1, the infection will die out in the long run
- when R0<1, the infection is able to spread in a population
what factors affect R0?
3
- duration of infectivity
- infectiousness
- number of susceptible people exposed to pathogen
what is the cut off size for an aerosol?
5μm
what is the difference between an aerosol and a droplet?
- aerosols are small enough to remain airborne for long periods of time
- droplets are larger so fall to the ground relatively quickly
what factors affect aerosol transmission?
3
- physiochemical properties of virus-laden aerosols (size, viral load and infectivity, other chemical components, pH value, electrical charge)
- viral determinants of virus survival and transmission (envelope and capside structure)
- environmental determinants of virus survival (temperature, humidity, pH, ventilation and airflow, salinity, surface materials, UV radiation)
