Wednesday, September 21, 2011

Biosafety Measures in the Clinical Laboratory

Biologic safety cabinets
Clinical laboratories are special, often unique, work environments that may pose identifiable infectious disease risks to persons in or near them. These infections have been recognized for many years. In a series of published early surveys, Pike and associates1-4 reported over 3,000 cases of laboratory-acquired infections, including brucellosis, tuberculosis, typhoid, streptococcal infections, and hepatitis. These incidents, along with considerable anecdotal information, suggest that most laboratory-acquired infections occur as a result of error, accident, or carelessness in the handling of a known pathogen; often the mode of transmission is unknown.
During the 1970s, in an effort to reduce the risks of infection in the laboratory, scientists devised a system for categorizing etiologic agents into groups based on the mode of transmission, type and seriousness of illness resulting from infection, availability of treatment (eg, antimicrobial drugs), and availability of prevention measures (eg, vaccination). The etiologic agent groupings were the basis for the development of guidelines for appropriate facilities, containment equipment, procedures, and work practices to be used by laboratorians. These guidelines, now referred to as biosafety levels 1 through 4, are published and regularly reviewed by the Centers for Disease Control and Prevention (CDC) and the National Institutes of Health (NIH).
Biosafety level guidelines recognize that facility design is important in providing a barrier to protect persons working in the facility as well as those in the community. An accidental release of certain airborne infectious agents could be catastrophic. To assist in planning and managing a laboratory, the CDC describes 3 facility designs based on functions in handling infectious agents.
Basic Laboratory
The first design, known as the basic laboratory, provides general space in which work is done with viable biosafety level 1 agents (eg, Bacillus subtilis, Naegleria gruberi), which are not associated with disease in healthy adults, and biosafety level 2 agents (eg, hepatitis B, salmonellae), which pose minimal potential aerosol hazard to laboratory personnel and the environment. Basic laboratories include those that use biosafety levels 1 and 2. While work is commonly conducted on the open bench, certain operations are confined to biologic safety cabinets. Public areas and general offices to which non laboratory staff requires frequent access should be separated from spaces that primarily support laboratory functions.
Biosafety level 2 used in the basic laboratory differs from biosafety level 1 in that:
1. Laboratory personnel have specific training in handling pathogenic agents and are directed by competent scientists;
2. Access to the laboratory is limited when work is being conducted;
3. Extreme precautions are taken with contaminated sharp items; and
4. Certain procedures in which infectious aerosols or splashes may be created are conducted in biologic safety cabinet or other physical containment equipment.
There is no specification for single-pass directional inward flow of air (a system in which air goes through the laboratory area once before being filtered) from a biosafety level 2 laboratory. However, because most microbiology laboratories also work with potentially hazardous chemicals, negative air pressure is usually present as well. There are published recommendations for preventing buildup of chemical vapors in laboratories, including use of chemical fume hoods and/or single-pass air when recirculation would increase the ambient concentration of hazardous materials.
Containment Laboratory
The containment laboratory has special engineering features that make it possible for laboratory personnel to handle aerosolized hazardous materials (eg, Mycobacterium tuberculosis, Coxiella burnetii, and St Louis encephalitis virus) without endangering themselves. More emphasis is placed on primary and secondary barriers to protect personnel in contiguous areas and the community from exposure to potentially infectious aerosols and to prevent contamination of the environment. This laboratory is usually described as a biosafety level 3 facilities.
The unique features that distinguish this laboratory from the basic laboratory are the provisions for access control and a specialized ventilation system. The containment laboratory may be an entire building or a single room (eg, for tuberculosis testing) in a basic laboratory. A containment laboratory is separated from other parts of the building by an anteroom with 2 sets of doors or by access through a basic laboratory area. Because of the potential for aerosol transmission, air movement is unidirectional into the laboratory (ie, from clean areas into the containment area), and all exhaust air is directed outside the building without any recirculation, or it undergoes high-efficiency particulate air (HEPA) filtration.
All procedures involving the manipulation of infectious materials are conducted within biologic safety cabinets or other physical containment devices. These facilities have solid floors and ceilings and sealed penetrations. They are designed and maintained to allow appropriate decontamination in the event of a significant spill. All waste from these laboratories must be rendered noninfectious before final disposal.
Maximum Containment Laboratory
The maximum containment laboratory has special engineering and containment features that allow activities associated with infectious agents (e.g., Lassa virus, Ebola virus) that are extremely hazardous to laboratory personnel or that may cause serious epidemic disease. This laboratory is considered a biosafety level 4 facilities. Although the maximum containment laboratory is usually a separate building, it can be constructed as an isolated area within a building. The laboratory's distinguishing characteristic is that is has secondary barriers to prevent hazardous materials from escaping into the environment. Such barriers include sealed openings into the laboratory, air locks or liquid disinfectant barriers, a clothing-change and shower room contiguous with the laboratory, a double-door autoclave, a biowaste treatment system, a separate ventilation system, and a treatment system to decontaminate exhaust air.
Within work areas of the facility, all activities are confined to class III biologic safety cabinets or class II biologic safety cabinets used by personnel wearing 1-piece positive-pressure body suits ventilated by a life-support system. Members of the laboratory staff have specific and thorough training in handling extremely hazardous infectious agents, and they understand the primary and secondary containment functions of the standard and special practices, the containment equipment, and the laboratory design characteristics. They are supervised by competent scientists who are trained and experienced in working with these agents.
All wastes are decontaminated before leaving the maximum containment laboratory, and the exhaust air is passed through HEPA filters. Except in extraordinary circumstances (eg, suspected hemorrhagic fever), the initial processing of clinical specimens and identification of isolates can be done safely at a lower level containment. The containment elements are consistent with the Occupational Safety and Health Administration Blood borne Pathogen Standard as well as those recommended by the National Committee for Clinical Laboratory Standards (M29-A).

Biologic Safety Cabinets
Various laboratory procedures generate aerosols that may spread biohazardous materials in the work area and pose a risk of infection to personnel. Biologic safety cabinets are used to prevent the escape of aerosols or droplets and to protect the research product from airborne contamination. These devices are distinct from horizontal or vertical laminar flow hoods, which should never be used for handling biohazardous, toxic, or sensitizing material. Chemical fume hoods also should not be used for biohazards as they are solely designed to protect the individual from exposure to chemicals and noxious gases. These chemical fume hoods are not equipped with HEPA filters. BSCs are designed to protect the individual and the environment from biologic agents and to protect the specimens and other materials from biologic contamination.
There are 3 general types of BSCs: class I, II, and III [F1] [F2] and [F3] There is 1 type of class I BSC. This cabinet is similar to a chemical fume hood with an inward airflow through the front opening. The exhaust air from the biologic safety cabinet is passed through a HEPA filter so that the equipment provides protection for the worker and the public. However, the specimens and other materials are potentially subject to contamination. Class I cabinets are not generally recommended for biohazard work.
Class II biologic safety cabinets are designed to protect personnel, the general public, and the specimen. The airflow velocity at the face of the work opening is at least 75 linear feet per minute (lfpm). Both the supply and the exhaust air are HEPA filtered. There are 4 types of class II cabinets (IIA, IIB1, IIB2, and IIB3). They differ in the amount of recirculation, downflow, and inflow. Usually, all but IIA are considered satisfactory for biohazard and toxic agents.
Class III cabinets are totally enclosed, ventilate cabinets of gas-tight construction, and offer the highest degree of protection from infectious aerosols. They also protect research materials from biologic contamination. Class III cabinets are most suitable for work with hazardous agents that require biosafety level 3 or 4 containment. All operations in the work area of the cabinet are performed through attached rubber gloves. The cabinets are operated under negative pressure. Supply air is HEPA filtered, and the cabinet exhaust air is filtered by 2 HEPA filters in series or HEPA filtration followed by incineration, before discharge outside of the facility.
Every day, new organisms are discovered that could potentially become pathogenic to the laboratory staff, patients, and visitors. It is up to the laboratory specialists in infection control, safety, and microbiology to recognize these potential diseases and handle the organisms according to the NIH's most-recent biosafety guidelines.

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