Download Handout 1 How do Infections Spread

The principles of infection prevention and control
Handout 1: How do infections spread?
Users of health and social care services are vulnerable to infections. In particular
infections such as influenza, MRSA (meticillin-resistant Staphylococcus aureaus), C.
difficile (Clostridium difficile) and norovirus can spread quickly and easily between
people in a health or social care environment such as a hospital or residential care
home. Knowing how infections spread is important in preventing and controlling them.
The chain of infection
A useful way to think about infection and the way it is spread is as a chain made up of a
number of links. All procedures and systems for preventing and controlling infection can
be viewed as methods to break the chain of infection. By removing one or more links,
you interrupt the process that allows infection to spread (see figure 1 on next page).
The links for the chain of infection are:
1. Pathogens (bacteria or viruses).
2. A suitable environment for pathogens to reproduce.
3. Transport for pathogens to be spread to the next person (also known as
transmission).
4. A route in to the body.
5. A route out of the body.
6. A next host to spread pathogens on to.
A next host
to spread
pathogens
on to
Pathogens
(bacteria or
viruses)
A suitable
environment
to reproduce
A route out
of the body
A route in to
the body
Transport for
pathogens
Figure 1: The links in the chain of infection
Understanding the chain of events
1. Pathogens include disease causing micro-organisms such as bacteria, viruses, fungi
and parasites.
2. A suitable environment means the conditions required by the pathogens to survive.
Different pathogens require different conditions to reproduce. Bacteria, for example
prefer warm, moist places to enable the cells to divide and multiply.
3. Transport/transmission is required because pathogens are not able to move
independently. They need to be transported from place to place and person to
person, either directly through, for example coughing sneezing or kissing, or via
hands or a contaminated object.
4. Routes in to the body could be through a natural opening, such as the mouth, nose,
or urethra, or through an unnatural opening, such as a cut or an insect sting, or a
tube that goes into the body, such as a urinary catheter.
5. Routes out of the body are exactly the same as routes in.
6. Infection spreads most easily to individuals who are vulnerable in some way, such as
young babies or older people, or those with a chronic condition. It is also more likely
to spread where lots of individuals are gathered together, for example in schools,
hospitals and residential homes.