9. Infection Prevention Flashcards
Describe the communicable nature of infections
•Many infections are transmissible - From a non-human source to humans - From person to person •Directly •Indirectly
What is a common source in terms of infection?
A common source outbreak is one in which a group of persons are all exposed to an infectious agent or toxin from the same source.
What are examples of common sources of infection?
- environmental: e.g. legionella pneumophilia
- food/ water e.g. food poisoning organisms - onward transmission possible
- animals e.g. rabies - onward transmission possible
- some pathogens can then be passed on from human to human
What are examples of infections that are passed on directly person to person?
Influenza, norovirus, neisseria gonorrhoea
What are examples of vectors?
Mosquitos
Define endemic disease
The usual background rate
Define outbreak
Two or more cases linked in time and place
Define epidemic
A rate of infection greater than the usual background rate
Define pandemic
Very high rate of infection spreading across many regions, countries, continents - global
What is the basic reproduction number?
R0 - the average number of cases one case generates over the course of its infectious period, in an otherwise uninfected, non immune population
What does it mean if R0 > 1 ?
Increase in cases
What does it mean if R0 = 1 ?
Stable number of cases
What does it mean if R0 < 1 ?
Decrease in cases - disease will die out as for every one case, there is less than one secondary case
What are examples of diseases with high basic reproduction numbers?
Measles, pertussis, diphtheria
What are causes for outbreaks, epidemics and pandemics?
- New pathogens - antigens, virulence factors, antibacterial resistance
- New hosts - non-immunes e.g. babies and young children
- New practice - social, healthcare
- place
Define infectious dose
a minimum number of microbes required for an infection to proceed
Compare person-to-person direct and indirect transmission
These pathogens are entirely person to person there are no animals or environmental factors involved.
Examples include influenza, norovirus and neisseria gonnorhoea.
In indirect transmission a vector is important e.g in the transmission of malaria from person to person using mosquitoes
What is an example of a micro-organism with a low infectious dose?
E Coli —> does not take many to cause infection - only 1 cyst can cause infection
Give two examples of micro-organisms with a high infectious dose?
Salmonella, cholera
What is the epidemic curve?
As the outbreak grows amongst susceptible people, number of infected people increase
Then as people recover, less susceptible people to infection so number of infected people decrease
What is the nature of small scale outbreaks?
Tend to have a stochastic nature
How can we intervene with pathogens and vectors?
- reduce/ eradicate pathogen - antibacterials/ disinfectants, decontamination, sterilisation
- reduce/ eradicate vector - eliminate vector breeding sites
How can we intervene with patients?
- improved health - nutrition, housing, medical treatment
- immunity - passive e.g. maternal antibody, IV immunoglobulin, active e.g. vaccination
- herd immunity
What is herd immunity?
When a majority of a population are vaccinated against a disease. This means that even people who have not been vaccinated are less likely to get it because there are fewer people to catch it from.
