It is a basic biosafety principle that all contaminated materials be decontaminated prior to disposal. Decontamination includes both sterilization (the complete destruction of all microorganisms, including bacterial spores) and disinfection (the destruction and removal of specific types of microorganisms). It is the responsibility of all laboratory workers to ensure the effective use of products for decontamination of materials, equipment, and samples from containment zones; of surfaces and rooms; and of spills of infectious materials. These procedures represent a critical containment barrier whereby failure in the decontamination procedure can result in occupational exposure to infectious agents and/or the unintentional release of agents from a containment facility. Chapter 15 of CBH provides crucial information on sterilization, disinfection, and decontamination.
All contaminated materials must be decontaminated before disposal or cleaning for reuse. The choice of method is determined by the nature of the material to be treated. This may include, but is not limited to, laboratory cultures, stocks and clinical specimens; laboratory equipment, sharps and protective clothing; and other items that have come into contact with infectious materials. Laboratory bench tops and surfaces are to be decontaminated after any spill of biological materials and at the end of the working day. Laboratory rooms and large pieces of equipment may also require decontamination (i.e., prior to servicing, maintenance, transfer to other settings or reassignment). Specific written protocols are available in the University’s Laboratory Hazardous Waste Management and Disposal Manual. Employees must be trained in all decontamination procedures specific to their activities and should know the factors influencing the effectiveness of the treatment procedure, as discussed briefly below.
Chemical disinfectants are used for the decontamination of surfaces and equipment that cannot be autoclaved (such as specimen containers and other items removed from containment); cleanup of spills of infectious materials, rooms and animal cubicles; and a variety of other items for which heat treatment is not feasible.
The initial choice of a chemical disinfectant depends upon the resistance of the microorganisms of concern. The most susceptible are vegetative bacteria, fungi and enveloped viruses. Mycobacteria and non-enveloped viruses are less susceptible, and bacterial spores, protozoan cysts and Prions are generally the most resistant. Consideration should also be given to practicability, stability, compatibility with materials and health hazards.
The effectiveness of the disinfectants can be influenced by a number of factors: presence of organic material (e.g., blood, serum, sputum) that decreases the effect of hypochlorites; temperature; relative humidity; concentration; and contact time. In some cases, it may be beneficial for laboratories to conduct in-use disinfectant efficacy testing to evaluate a product’s performance in the field, under conditions of use. The use-dilution test is a basic method to evaluate surface disinfectants that involves the artificial contamination of a surface and immersion in the appropriate dilution of the disinfectant for a specific amount of time. Finally, the surface is dipped in a fresh sterile medium that does not contain disinfectant and then checked by incubation to determine whether all microorganisms have been killed. A similar protocol can be used to verify the effectiveness of disinfectants used in discarded containers: an inoculum is added to the disinfectant solution, which after a predetermined contact time, and an aliquot is examined for growth by incubation. The active components of disinfectants belong to relatively few classes of chemicals, and understanding the capabilities and limitations of each class of chemicals (e.g., hypochlorites, quaternary ammonium compounds, phenolics, iodines, alcohols) will allow the choice of a product based on relative effectiveness.
Gaseous Decontamination of Rooms
Gaseous decontamination of rooms is generally only necessary at containment levels 3 and 4 under particular circumstances (e.g., after a spill or accidental release of infectious materials, for removal of large equipment items from containment, before maintenance work on contaminated systems, before retesting of HVAC control systems).
Because of the potential for exposure to the hazardous chemicals used (e.g. formaldehyde), gaseous decontamination of rooms should be done only by highly trained personnel. The two-person rule should always apply to this operation, and both individuals should be trained and fitted in the use of appropriate respiratory protection.
Gamma irradiation (e.g., 60Co) can be used for the decontamination of heat-sensitive materials and is an effective means of decontaminating chemicals and solvents removed from a containment facility. The efficacy of the treatment technology depends on the penetration of the treated items by gamma irradiation and, therefore, on the density of the treated substance as well as the strength of the irradiation source.
Microwave irradiation is not widely used for decontamination in containment facilities. As in steam autoclaving, heat is the critical factor for eliminating viable microorganisms. The factors that affect microwave treatment include the frequency and wavelength of the irradiation, the duration of exposure and the moisture content of the material to be decontaminated.
The use of ultraviolet (UV) germicidal lamps is strongly discouraged due to their limited effectiveness at disinfecting the inside of BSCs. Personnel wishing to use UV irradiation in BSCs should receive training on the safe work practices required and the hazards of UV radiation beforehand. UV should not be relied upon as the sole method of decontamination for materials removed from containment facilities. UV has limited penetrating power and is primarily effective against unprotected microbes on exposed surfaces or in the air. It can be effective in reducing airborne and surface contamination provided that the lamps are properly cleaned, maintained and checked to ensure that the appropriate intensity is being emitted.