Infection control WORLD OF MICROBIOLOGY AND IMMUNOLOGY310•
resistant to the compounds. Examples of such resistance
includes the chronic Pseudomonas aeruginosalung infections
experienced by those with cystic fibrosis and infection of arti-
ficially implanted material, such as urinary catheters and heart
pacemakers.
Bacteria and viruses can also evade immune destruction
by entering host cells and tissues. Once inside the host struc-
tures they are shielded from immune recognition.See alsoAntibody and antigen; Antibody formation and kinet-
ics; Antibody-antigen, biochemical and molecular reactions;
Bacteria and bacterial infection; Bacterial adaptation; Biofilm
formation and dynamic behavior; Immune system; Immunity,
active, passive and delayed; Immunity, cell mediated;
Immunity, humoral regulation; Immunodeficiency;
Microbiology, clinical; Viruses and responses to viral infectionIInfection controlNFECTION CONTROL
Microorganismsare easily transmitted from place to place via
vectors such as insects or animals, by humans that can harbor
the infectious organism and shed them to the environment, and
via movement through the air (in the case of some bacteria,
yeast, and viruses). Microorganisms can adapt to antimicro-
bial treatments (the best example being the acquisition of
inheritable antibiotic resistanceby bacteria). Thus, the poten-
tial for the spread of infection by disease-causing microbes is
substantial unless steps are taken to limit the spread. Such
strategies are collectively termed infection control.
For many microorganisms, particularly bacteria, contact
transmission is a common means of spread of infection. This
can involve the fecal-oral route, where hands soiled by expo-
sure to feces are placed in the mouth. Day care workers and
the infants under their charge are a significant focus of such
Escherichia coliinfections. As well, touching a contaminated
inanimate surface is a means of transmitting an infectious
microorganism.
The contact route of transmission is the most common
route in the hospital setting. Various steps can be taken to con-
trol the spread of infection through contact with contaminated
surfaces. Proper handwashing, in fact, is the single most effec-
tive means of preventing the spread of infection. Thorough
handwashing prevents spread of bacteria to others and also
prevents contaminationof work or food preparation surfaces.
The operating theatre is an example of a place where the
importance of infection control measures is apparent. In the
nineteenth century, before the importance of hygienic proce-
dures was recognized, operations were used as a last resort
because of the extremely high mortality rate after surgery.
Pioneering efforts by scientists such as Joseph Listermade
operating rooms much cleaner, which resulted in a drop in the
death rate attributable to surgically acquired infections. In the
present day, operating rooms are places where personal
hygieneis meticulous, instruments and clothing is sterile, and
where post-operative clean up is scrupulous.
In hospitals and particularly in research settings, the
control of infections involves the use of filters that can beplaced in the ventilation systems. Such filters prevent the
movement of particles even as small as viruses from a con-
tainment area to other parts of a building. Work surfaces are
kept free of clutter and are exposed to disinfectant both
before and after work with microbes, to kill any transient
organisms that may be on the inanimate surface.
Laboratories often contain containment structures called
fume hoods, in which organisms can be worked with isolated
from the airflow of the remainder of the lab. Even the nature
of the work surface is designed to thwart infection. Surfaces
are constructed so as to be very smooth and to be watertight.
The presence of crevasses and cracks at the junction between
surfaces are ideal spots for the collection and breeding of
infectious microorganisms.
Some infectious microorganisms can be transferred by
animal or insect vectors. One example is the viral agent of
Yellow Fever, which is transmitted to humans via the mos-
quito. Control of such an infection can be challenging.
Typically a concerted campaign to kill the breeding popula-
tion of the vector is required, along with measures to protect
people from those vectors that might escape the eradication
campaign. To use the Yellow Fever example, spraying in
mosquito breeding sites could be supplemented with the use
of mosquito netting over the beds of people in particularly
susceptible regions.
Another strategy of infection control is the use of
antimicrobial or antiviral agents in an effort to either defeat an
infection or, in the case of vaccines, to protect against the
spread of an infection. Antibioticsare an antimicrobial agent.
They have been in common use for less than 75 years, and
already history is showing that antibiotics achieve success but
that this success should not be assumed to be everlasting.
Bacteria are proving to be adept at acquiring resistance to
many antibiotics. Indeed, already strains of enterococci and
Staphylococcus aureusare known to be resistant to virtually
all antibiotics currently in use.
Immunizationagainst infection is a widely practiced
and successful infection control strategy. Depending upon the
target microbe, the vaccinationprogram may be undertaken
to prevent the seasonal occurrence of a malady such as
influenza, or to eradicate the illness on a worldwide scale. An
example of the latter is the World Health Organization’s effort
to eradicate polio.
One breeding ground for the development of resistant
microbial populations is the hospital. Antibiotics and disinfec-
tants are an important part of the infection control strategy in
place in most hospitals. Bacteria are constantly exposed to
antibacterial agents. The pressure to adapt is constant.
The degree of infection control is tailored to the insti-
tution. For example, in a day care facility, the observance of
proper hygiene and proper food preparation may be adequate
to protect staff and children. However, in a hospital or nurs-
ing home, where people are frequently immunocompro-
mised, additional measures need to be taken to ensure that
microbes do not spread. Such measures can include regular
disinfectionof surfaces, one-time use of specific medical
equipment such as disposable needles, and well-functioning
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