[Music]
[Narrator:] Laboratory-associated infections
continue to be serious hazards for people engaged in research or clinical diagnostic work.
The magnitude of the problem is apparent from data accumulated during the last 50 years.
Since 1925, some 4,000 reported infections
have endangered the health of laboratory workers.
160 of these infections
resulted in death for the individuals involved.
The majority of the laboratory infections
occurred at institutions engaged in research
or clinical diagnostic work.
The people involved were primarily trained professionals,
people most knowledgeable about laboratory hazards.
The meaning is clear.
Infectious hazards can only be reduced
by carefully following appropriate procedures.
This presentation has been prepared
to provide the knowledge you need
to reduce biological hazards in the laboratory.
[Music] [Bureau of Laboratories presents]
[Controlling Infectious Aerosols]
[Precautions in Microbiology]
Of 4,000 cases studied during the past 50 years,
only 20% have been identified as resulting from known causes.
80% of the cases investigated resulted from unknown causes.
Most investigators concluded that infections from these unknown causes
were due to routine microbiological procedures,
including procedures which resulted in producing aerosols which contain microbes.
These aerosols were found to be
the principal agents contaminating the laboratory environment.
Studies conducted since 1950
suggest that the following questions must be considered:
What forms do potentially infectious aerosols take?
What factors determine whether a laboratory worker becomes infected?
What determines the relationship between these factors?
We also need to know what common microbiological procedures
are likely to generate infectious aerosols.
We may also ask what procedures
are likely to be hazardous in work with experimental laboratory animals.
We have posed these questions to add emphasis to key points
to be explored in this presentation.
[Aerosol Droplets]
In identifying aerosols produced by routine procedures as principal contaminants of the laboratory environment,
two distinct forms have been described.
One kind of aerosol is primarily composed of large droplets,
larger than five microns.
The second kind of aerosol consists mainly of droplet nuclei.
These are tiny solid particles
whose usual size is less than five microns.
The two forms of aerosols contaminate the laboratory environment in contrasting ways.
First, consider the aerosol composed primarily of large droplets.
These large droplets settle in a relatively short time
and contaminate work surfaces or skin.
The droplet nuclei found in the second type of aerosol form
as a result of almost instantaneous dehydration.
In contrast to large droplets, droplet nuclei
may remain indefinitely suspended in the air,
drifting about with even slight air currents.
These droplet nuclei may contain only one
or a few microorganisms.
Four factors determine whether you, the laboratory worker,
will become infected by contact with large or small droplet aerosols.
[Factors]
Factors determining infection are: extent of contamination,
route of infection,
virulence of the organism,
and host susceptibility.
Interaction between these four factors will vary with each pathogen handled.
This is why the microbiologist must have a detailed working knowledge
of any disease-producing agent he or she is to study.
The first factor on our list is extent of contamination.
That is, how many microorganisms contaminate the air
or surface with which the microbiologist comes in contact?
These may be measured with air samplers or liquid impingers.
The second factor is route of infection.
The route may be by inhalation, ingestion,
penetration of the skin, or accidental inoculation.
The inhalation or airborne route
occurs in diseases like tuberculosis.
Such diseases are spread by inhalation of bacilli
contained within the nuclei.
Each droplet nucleus is less than five microns in size.
Tuberculosis and other diseases transmitted primarily by droplet nuclei
are less likely to be of concern when only surface contamination occurs.
Ingestion is another frequent route of infection.
Salmonellosis, shigellosis,
or other enteric diseases are commonly spread in this way.
Touching contaminated surfaces can result in finger-to-mouth transmission
of these infectious agents.
Penetration of unbroken skin
is also an important route of infection.
Tularemia is an example of an infection
that may result from penetration of unbroken skin
as well as from accidental inoculation or inhalation.
Still another route of infection
is through accidental inoculation,
which may occur as a result of animal bites,
ineedle noculations, or punctures by broken contaminated glassware.
We have explored two of the four factors determining infection:
extent of contamination and route of infection.
The other two factors are virulence of the organism
and host susceptibility.
When considering virulence, remember
that some infections may be initiated with one
or just a few organisms.
Others may require large inocula to initiate infection.
Finally, host susceptibility
will determine the severity of the illness resulting from infection.
Increased resistance to infection can be achieved through vaccination.
We must assure that personnel are properly immunized.
We have now identified four infection-determining factors:
extent of contamination, route of infection,
virulence of the organism, and host susceptibility.
The importance of these factors varies from one pathogen to another.
We shall now look more closely at the role of aerosols
as a cause of laboratory infections.
Potentially infectious aerosols are formed
when common laboratory tools are used.
Care must be taken with procedures involving the inoculating loop,
pipette,
syringe, and needle.
Frequently, aerosols are produced when the inoculating loop
is used to streak an agar plate having a rough surface.
Such roughness occurs where bubbles remained in the agar surface while it hardened.
Aerosol formation may be significantly reduced by using only smooth,
bubble-free agar media.
The aerosols may be further reduced by spreading the inoculum
with a sterile, bent glass rod.
Using the bent glass rod reduces aerosols as much as 65%,
even on rough agar.
The inoculating loop is often sterilized in the flame of a Bunsen burner.
When the hot loop is immediately touched to colonies on solid media
or when the hot loop is inserted into a liquid microbial culture,
the sizzling creates a dangerous aerosol.
Aerosol formation may be reduced as much as 99%
by allowing the loop to cool before using it.
Infectious aerosols also result from the improper use of pipettes.
When the last drop is forcibly expelled from a pipette,
the bursting bubble generates a dangerous aerosol.
To minimize this problem,
drain contents from the pipette by gravity flow.
This reduces aerosol production by as much as two thirds.
The pipette is frequently used to mix culture suspensions in a tube.
This often results in aerosol-generating bubbles forming at the liquid surface.
You may reduce bubble production by using one of several available test tube mixers.
Here, mixing is centrifugal,
forcing organisms toward the walls of the container
rather than producing bubbles.
When the tube is kept closed during mixing,
the nearly saturated atmosphere in the tube
greatly minimizes droplet nuclei formation.
Some large droplets, however, may escape as the cap is removed.
Every microbiologist has at some time
seen a drop of culture suspension fall from a pipette tip.
The amount of potentially infectious aerosol thus formed
varies with the type of work surface.
The harder the surface, the greater the splatter.
You can reduce such aerosols by as much as 90%
by placing a towel soaked in disinfectant
on the work surface.
Procedures involving the syringe and needle
are also potential sources of aerosols.
Do not use a syringe as a substitute for a pipette.
Accidentally dislodging a needle from a syringe can be especially dangerous.
To prevent this kind of accident,
use only locking syringes.
When a needle is removed from a rubber stoppered vial,
the needle will vibrate,
producing an infectious aerosol.
Wrapping the stopper and needle with alcohol-soaked gauze
considerably reduces these aerosols.
Expelling air from a partially-filled syringe
also creates an aerosol.
This procedure should be done only
when the needle is covered with alcohol-soaked gauze.
Some laboratory procedures require handling and injection of experimental animals.
Laboratory animals should always be handled by trained personnel.
Animals must be properly restrained during inoculation.
When animals are inoculated,
a portion of the inoculum often leaks back onto the animal's skin.
When the animal is returned to its cage,
organisms on the skin contaminate bedding.
These organisms may then be carried throughout the room on air currents.
Swabbing the injection site with antiseptic both before and after injection
will reduce airborne organisms by 30%.
During this presentation,
we have explored ways to reduce infectious aerosols in the laboratory.
We have seen how large droplets and droplet nuclei aerosols are formed in common laboratory procedures
and may result in contamination.
Proper use of the inoculating loop, pipette,
needle, and syringe will significantly reduce this contamination.
Many infectious incidents stem from the use of techniques which create aerosols.
By reducing aerosols as depicted in this presentation,
you can eliminate many of the infections
that commonly occur in the laboratory.
[Music] [Controlling Infectious Aerosols]
[Precautions in Microbiology]
[Technical Advisors: John E. Forney, PhD George P. Kubica, PhD]
[Produced by the National Medical Audiovisual Center]
[for Laboratory Training and Consulation Division Bureau of Laboratories, CDC]