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Chain of infection
Objectives: Chain of Infection
1. List the factors involved in the Chain of Infection
2. State the key role of the nurse in relation to the chain of
infection
3. Define the term ‘pathogen’
4. Briefly explain what is meant by the term ‘reservoir’
5. Outline the distribution of body flora, giving an example from
each site
6. Briefly explain what is meant by the term ‘portal of exit’
7. Define ‘mode of transmission’, differentiating between contact,
common vehicle, airborne and vector borne
8. Briefly explain what is meant by the term ‘portal of entry’
9. Outline the means by which the skin, mucous membranes, the
GI tract and the GU tract protect the body from infection
10. Explain what is meant by susceptible host
Objectives: Introduction to Microbiology
1. Briefly explain the importance of understanding
microbiology in terms of the nurse’s role
2. List 4 types of micro-organisms
3. Label a diagram of a typical bacterium (indicating
nucleic acid, cytoplasm, cell membrane, cell wall,
capsule, ribosome, storage material, flagellum, pili
4. Briefly explain the function/s of the above structures
5. State the significance of the Gram negative and Gram
positive terms
6. State three features which may be used to classify
bacteria
7. List four distinct requirements for bacterial growth
Objectives: Introduction to Microbiology
8. Name the main method by which bacteria reproduce
9. Briefly explain the difference between viruses and
other microbes
10. Give three example of common viruses
11. Briefly explain the growth requirements for viruses
and method of reproduction
12. Outline the main differences between fungi and
bacteria
13. State which type of organism is responsible for:
hospital acquired infections, community illnesses,
mycoses
Chain of Infection
The infective process involved in the development
of disease hinges upon a complex interaction
between:
• Pathogen
• Reservoir
• Portal of exit
• Mode of transmission
• Portal of entry
• Susceptible host
Together these factors are termed:
The Chain of Infection
Pathogen
Definition: Disease producing micro-organism
• Question: Are all microbes harmful?
• Question: Are some microbes beneficial?
• Question: Are these beneficial organisms
ever harmful?
• What is the name for microbes that colonise
the human body in health?
Breaking the Chain
Given the right circumstances ,
potentially all micro-organisms may
cause disease
Nurses need to reduce this risk by:
* Recognising the components and
* Breaking the chain in as many
places as possible
Reservoir
Definition: a location or environment
where a micro-organism can survive
and multiply
Reservoirs may be:
* Animate e.g. human, animal,
bird, plant OR
* Inanimate e.g. food, water,
air, soil, excreta, dust and
fomites such as bedding or
toys
Distribution of Normal Body Flora
Portal of Exit
Definition: Place from which
the micro-organism escapes
the reservoir e.g.
- Sputum
- Blood
- Vaginal secretions
- Semen
Mode of Transmission
Definition: Route via which the microorganism is transmitted to the host
Can be classified as:
a) Contact
b) Common vehicle
c) Airborne / Droplet spread
d) Vector borne
e) From mother to baby
Mode of Transmission
Contact
Direct
e.g. skin
to skin
Indirect
e.g. shared
needles
Mode of Transmission
Common vehicle
Via a common
source such as
contaminated
food or water
Mode of Transmission
Airborne
Through contact with
infected secretions
produced when a
person talks or sneezes.
Particles may be
contained in:
* large droplets
* droplet nuclei / dust
Mode of Transmission
Vector borne
• Via insects or animals e.g.
malaria spread by mosquitoes
Mode of Transmission
From Mother to Baby
Pre-natal
Peri-natal
Post-natal
Portal of Entry
Definition: Route via which
micro-organisms enter the host
This may occur via:
Skin
Mucous membranes
Gastro-Intestinal tract
Genito-Urinary tract
Portal of Entry: Skin
When intact – the skin
is a very important
barrier
The skin:
… Acts as a mechanical barrier
… Has a slightly Acid pH
… Has skin flora
All the above provide a hostile barrier for
pathogenic organisms
When breached – microbes may enter
Portal of Entry: Mucous
membranes
Some protection via:
… muco-ciliary clearance
... lysozyme
… secretion of a special antibody
However, ulceration,
or loss of cilia can lead
to microbes gaining entry
via this route
Portal of Entry: GI Tract
The GI Tract is protected by:
… Acid pH of the stomach
… Pancreatic enzymes
… Bile
… Normal flora of the
tract
… Peristaltic action
of the gut
Portal of Entry: GU Tract
The GU Tract is protected by:
… Frequent flushing of urine
… Secretion of Ig A
… Antibacterial action
of sperm
… Acid pH of vagina
… Normal flora of the
tracts
Susceptible host
• Definition: An
individual who
succumbs to the
effects of invading
microbes due to
breaches in exterior
defences (e.g. skin or
mucous membranes)
and / or an inability to
mount an immediate /
sustained specific
immune response
Preventing the spread of infection:
Role of the Nurse
Disruption and blockage of chain
of infection
Protection of
susceptible patients
Prevention of Infections
Primary
Increase the resistance of the
patient
Interrupt the chain of infection
Restrict the spread of infection
Secondary
Detecting disease at earliest possible time to:
Begin treatment
Stop progression
Protect others
Tertiary
Limit the progression of disability
Treat symptoms and rehabilitate (varies with each specific
disease)