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Health Advisory Information
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 Health Advisory Information
Nosocomial infection
Nosocomial infections are infections acquired directly or indirectly
in a medical setting. The probability of a microorganism causing
infection in a host is dependent upon the dose (number of microorganisms),
a receptive host site of contact with the organism, time of contact
(sufficient for multiplication or not) and the virulence of the
organism.
The source(s) of the infecting agents may be patients, staff
or visitors and may include:
- persons with acute diseases,
- persons in the incubating or window period of a disease or
- persons who are colonised or chronic carriers of the infecting
agent
- the person's own endogenous flora,
- inanimate objects including equipment and medications.
Susceptible host
Resistance to infection varies depending upon underlying medical
conditions and other factors that may compromise a person's immune
status. Trauma, surgical procedures, anaesthesia, invasive indwelling
devices, and therapeutic and diagnostic procedures render a person
more susceptible to infection. Immunocompromised patients
are at increased risk of infection from both their own flora (endogenous)
as well as other sources (exogenous). Susceptibility to infection
depends on the severity and duration of immunosuppression. They
may be particularly susceptible to environmental contaminants
such as Legionnaires disease or Aspergillus. Where invasive medical
procedures are involved, consideration should be given to placing
patients at the start of the operating schedule. If considerable
immunosuppression or neutropenia is present the Additional Precaution
of single room accommodation is desirable.
Routes of transmission
- Direct contact transmission involves direct physical
transfer of microorganisms from an infected or colonised person
to a susceptible host. Indirect contact transmission involves
the contact of a susceptible host with a contaminated inanimate
object, such as contaminated instruments or equipment.
- Droplets are generated during coughing, sneezing, talking,
and during certain procedures such as suctioning and bronchoscopy.
Transmission occurs when droplets containing microorganisms come
in contact with the conjunctiva, nasal mucosa or mouth of a susceptible
person. Droplet distribution involves close association, usually
1 metre or less.
- Airborne transmission occurs by dissemination in the
air of either droplet nuclei or dust particles containing the
infectious agent. Microorganisms carried in this manner can be
widely dispersed via air currents and can remain airborne for
long periods before being inhaled by the susceptible host.
- Vehicle transmission applies to microorganisms transmitted
by contaminated food, water, drugs, blood or body fluids.
- Vectorborne transmission occurs when mosquitoes, flies,
rats or other vermin transmit microorganisms
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