Scientific exploration
is not without hazards. Each year’s these explorers contract infectious disease
because of accidental exposure to pathogens in laboratories. Over 4000 cases of
laboratory associated infections have been recorded with more than 160
fatalities.
The Centers for Disease
Control and Prevention has defined which microbes currently represent the
greatest hazard I the laboratory and has classified etiologic agents into four
categories. Class 1 contains agents that pose little risk of serious disease.
These include Staphylococcus epidermidis and many other members of the normal
flora. Microbes in class 4 are the most dangerous and require the highest
degree of containment. The plague bacillus is a class 4 bacterium.
The greatest number of
laboratory infections has occurred among persons engaged in research
activities. Fewer than 33% of these infections have been reported as occurring
in diagnostic laboratories. This perhaps reflects the unanticipated hazards of
handling newly discovered, poorly understood or previously unencountered
microbes. In a dramatic incident that occurred in Marburg, Germany in 1967, 31
persons handling the tissues of African green monkeys were infected by a
previously unknown virus in the tissue. Six of these victims died. Researchers
are microbiogy’s “test pilots”, and many unexpected hazards will likely surface
during their preliminary investigations. All persons who handle pathogenic
microorganisms are at risk of infection.
Most laboratory
associated infections are acquired by contact with infections aerosols. Random
air sampling demonstrates that common laboratory manipulations release
microorganisms into the atmosphere. Infectious aerosols are created by blowing
out a pipette or by removing a stopper.
Aerosols probably
account for the many laboratory associated infections that occur in the absence
of an identifiable accident. The centrifuge is also an important source of
infection and has accounted for at least four fatalities. Infected experimental
animals may discharge contaminated respiratory droplets into air. In addition
bites and scratches from these animals occasionally cause infection. Mouth
pipetting is one of the most hazardous of all laboratory manipulations,
resulting in numerous cases of typhoid fever, tularemia, scarlet fever,
hepatitis and influenza. Accidental inoculation with needles and syringes
accounts for many laboratory associated infections, such as HIV. Spills of
infectious materials are also implicated.
Laboratory associated
infections can be reduced by immunizing employees, establishing and enforcing
rules for safe laboratory practices, and using protective equipments. Good
hygiene, especially hand washing after exposure to clinical specimens or
laboratory cultures is essential. Biological safety cabinets are designed to
contain infectious aerosols at the source. Sealable centrifuge tubes of unbreakable
plastic minimize the possibility of leaks or breakage during high speed spins.
Hand operated suction devices eliminate the need for mouth pipetting.
Experimental animals can be properly housed to control airborne infection. Properly
designed laboratories provide adequate space, restricted access to areas where
highly infectious systems that being used and ventilation systems that
encourage the flow of air into areas where infectious aerosols may be
generated. Such ventilation systems however protect only persons outside the
laboratory. Adherence to universal precautions will also minimize transmission
of infectious agents.
Gloves should be worn
by all workers exposed to blood, body substances, or cultures of highly
infectious pathogens. Masks, gowns and protective eyewear may be necessary if
aerosols or spills are likely. In the final analysis, biological safety depends
on the attitude and conduct of the individual worker.
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