THE APPLICATION OF DISINFECTION AND STERILIZATION TO INFECTIOUS WASTE MANAGEMENT Eugene C. Cole, Dr.P.H. School of Medicine University of North Carolina, Chapel Hill, NC The application of the principles of disinfection and sterilization to effective infectious waste (IW) management must be viewed carefully. While in general, both processes involve the inactivation of microbial forms, the methods for achieving suitable disinfection and sterilization for the on-site treatment of infectious wastes are very limited. I might mention that on-site treatment has 3 potential advantages:.assurance that wastes are properly treated, (2) minimization of (1) potential risk to personnel as material moves through the waste stream, and (3) cost-effectiveness. Disinfection A disinfectant can be described as an agent, usually chemical, which destroys disease or other harmful microorganisms except, ordinarily, bacterial spores. It refers to substances applied to inanimate objects. Disinfectants may inactivate cells in a variety of ways including cell wall and cytoplasmic membrane damage, electron transport interference, and the coagulation of proteins and nucleic acids. While indeed, disinfection is normally a chemical process, it is not the only one. Ultraviolet (W) radiation has long been popular for the inactivation of airborne and surface microbes within the close vicinity of the -. generating lamp. UV radiation however, provides poor penetrability and is therefore not effective as a means of IW treatment.
Chemical disinfection is appropriate for the inactivation of liquid wastes, such as cultures of etiologic agents, associated biologicals, and human blood and blood products. It can also serve to decontaminate some solid infectious wastes in a small clinic or office laboratory where contaminated swabs, disposable culture loops, etc., are placed in jars of disinfectant when steam sterilization or incineration are unavailable. The ideal disinfectant, in addition to being microbicidal, should possess the characteristics listed in Table 1. Obviously, there is no ideal disinfectant, so decisions must be made as to which factors are most important in regard to the environment in question. Additionally, in assessing the efficacy of a chemical disinfectant, one must consider the important factors listed in Table 2. When selecting a suitable disinfectant, consider first the type or types or infectious agents that are of concern. Next, consider those products with demonstrated efficacy against those agents. This warrants becoming knowledgeable by reading and understanding product labels and literature and consulting other appropriate references. Normally it is inadequate to pour liquid waste (other than very small amounts) into a disinfectant solution. Preferably, an amount of concentrated disinfectant is placed into an appropriate container so that when the liquid waste is added, the final use-dilution will be that which is recommended. Mixing may be required. Following approximate inactivation, or at the end of the day, the container is emptied into
~~ Table 1. Characteristics of an Ideal Disinfectant Microbicidal Easy to use Detergent activity Non - toxic Non-irritating Harmless to surfaces Rapid action Activity in presence of organic matter Activity in presence of hard water Stability Residual activity Inexpensive
~ ~~~~ Table 2. Factors Affecting Disinfectant Efficacy Hydrogen in concentration Concentration Exposure time Presence of interfering substances Temperature Numbers of microorganisms Types of microorganisms
the sanitary sewer system (check local codes), and the system is flushed with tap water to dilute the disinfectant and avoid damage to plumbing. Solid waste items that have been decontaminated may then be regarded as non-infectious trash and disposed of accordingly. One should always remember that chemical disinfectants are toxic, and the use of proper personal protective equipment is recommended. Classes of Disinfectants The following are the most commonly used classes of chemical disinfectants : A. Alcohols. (60-90%) Advantages - bactericidal, tuberculocidal, virucidal (except isopropanol and against hydrophilic viruses), non-staining, non-irritating, rapid action. Disadvantanes - non-sporicidal, organic matter interference, incompatible with rubber and some plastics, highly flammable, relatively expensive. B. Quaternary Ammonium Compounds. Advantanea - bactericidal (especially against gram-positive organisms), virucidal (against lipophilic viruses), fungicidal, pleasant odor, inexpensive. pi sadvantu - non-tuberculocidal, non-sporicidal, organic matter interference, non-virucidal (against hydrophilic viruses).
C. Phenolics. Advantapes - bactericidal, fungicidal, tuberculocidal, inexpensive. Disadvantapes - questionable virucidal activity, nonsporicidal, toxic, skin irritant, unpleasant odor, D. corrosiveness. Iodophors. Advantapes - bactericidal, virucidal, fungicidal, detergent action, storage stability. Disadvantanes - prolonged exposure for tuberculocidal and sporicidal activity, corrosiveness, inactivation by organic matter, relatively expensive. E. Gluteraldehydes. Advantaees - bactericidal, virucidal, fungicidal, tuberculocidal, sporicidal, lack or organic matter interference, generally non-corrosive. Disadvantaeeg - irritant, limited shelf life, expensive. F. Hypochlorites. (2 500 ppm free available chlorine) Advantaees - bactericidal, virucidal, tuberculocidal, fungicidal, inexpensive. D i s advantane s - non-sporicidal, toxic, corrosive, bleaching agents. G. Hydrogen Peroxide. (2 3%) Advantages - bactericidal, virucidal, tuberculocidal, fungicidal, sporicidal. Disadvantaees - corrosive, expensive.
Chemical Inactivation of HIV (AIDS virus) The AIDS virus has been found to be extremely susceptible to chemical disinfection. Disinfectants used in lower than normal concentrations and yet able to inactivate lo5 HIV during a 10 min exposure at room temperature include: ethyl alcohol, isopropyl alcohol, sodium hypochlorite (50 ppm), phenolics, and hydrogen peroxide. Chemical Inactivation of HeDatitis B virus 6 High concentrations (10 ) of hepatitis B virus were found to be inactivated within 10 min at 20C by sodium hypochlorite (550 ppm), alkaline glutaralhdehyde (2%), glutaraldehyde-phenate (0.13%/0.44%), isopropyl alcohol (70%), and iodophor (80 ppm).
Sterilization Sterilization is the act or process, physical or chemical, which destroys all forms of life, especially microorganisms. Common sterilization techniques include steam heat, dry heat, ethylene oxide, and ionizing radiation. Of all the methods, heat, and particularly moist heat, is the most reliable and widely used. Ethylene oxide may present a carcinogenic, mutagenic, genotoxic, reproductive, neurologic, and sensitization hazard to personnel and is not recommended for IW treatment. Drv heat inactivation may be applied to solid infectious waste. As sterilization times are prolonged, however, and energy requirements are extensive, dry heat treatment of IW is not preferred. Ionizing radiation is an effective, low temperature sterilization method that is used extensively for a wide range of medical products. Because of its high cost it is only suitable for large scale sterilization. In considering all of the aforementioned sterilization methods, steam sterilization is preferred. Moist heat destroys microorganisms by the irreversible coagulation and denaturation of enzymes and structural proteins. The basic principle of steam sterilization, as accomplished in an autoclave, is to expose each item to direct steam contact at the required temperature and pressure for the specified time. Thus, there are four parameters of steam sterilization: pressure, temperature, time, and steam. Recognized exposure periods for sterilization of clean wrapped supplies (not infectious waste) are 30 min @ 121C in a gravity displacement sterilizer, and 4 min @ 132C in a prevacuum unit. At
constant temperatures, sterilization times vary depending on the size and type of load as well as the sterilizer type. In the gravity displacement unit, steam is admitted to the top of the chamber and because steam is lighter than air it forces air out the bottom of the chamber through the drain vent. Such autoclaves are primarily used to process culture media, water, pharmaceutical products, infectious waste, and non-porous articles whose surfaces have direct steam contact. For gravity displacement units, the penetration time is prolonged because of incomplete air elimination. High speed prevacuum sterilizers are similar to the gravity displacement type, except they are fitted with a vacuum pump to insure air removal from the sterilizing chamber and load before the steam is admitted. The advantage is nearly instantaneous steam penetration, even into porous loads. Autoclave monitoring is an essential part of the steam sterilization process. This includes in-use monitoring of temperature and pressure. Periodic preventive maintenance should include calibration of gauges and indicators. Biological indicators (using spores of Bacillus stearothermodhilus) should be run with actual loads on a daily or weekly basis depending on frequency of use. In 1982, Rutala et al. published data from a study of a gravity displacement steam autoclave that was tested to determine the operating parameters that affected sterilization of microbiological waste. Commercially available 1.5 mil polyethylene biohazard bags were used. They were tested in two modes: (1) in the open position, with the sides of the bag folded down to expose the top layer of petri plates, and (2)
with the opening in the bag loosely constricted with a twist tie. Four holes were punched in the tips of all twist tied bags. Loads were tested both with and without 500 ml of water added to the bags. 5, 10, and 15 lb. loads of contaminated petri dishes were tested. They contained 67, 136, and 205 plates, respectively. An average of 85% of the plates were contaminated with viable bacteria. The waste bags were placed into shallow stainless steel (ss) or polypropylene (pp) containers. The bags were monitored for time-temperature profiles by a digital potentiometer, and for sterilization efficacy by a biological indicator (spores of E. stearothermodhilus) within the load. At the end of the cycle, contents were sampled and cultured for viable microbes, both aerobically and anaerobically. Bacteria included Escherichia coli, StaDhvlococcus auxeus, StaDhvlococcus edidermidis, Klebsiella pneumoniae, and species of Acinetobacter, Enterobacter, Pseudomonas, Proteus, Streptococcus, and Bacillus. When 5 lbs of microbiological waste in ss containers with or without water, or pp containers with water was exposed to a steam sterilizing cycle of 30 min, no growth of vegetative or sporeforming bacteria occurred. In a pp container without water, all organisms were killed after a 45 min cycle. When 10 lbs of microbiological waste was tested in ss containers with water, 121C was reached in 45 min, and all organisms except the indicator spores were killed. Without water at 45 min, all organisms with the exception of the indicator spores were killed, but the temperature within the load did not reach 121C. Utilizing the ss containers, either with or without water, the indicator spores were not killed until a 90 min cycle was used. When the pp containers were used, either with or without water, 121C could not be
reached and indicator spores survived even when a 90 min cycle was used. All other organisms were killed after 45 min in the presence of water, and after 60 min without water. The 15 lb load data were essentially the same as for the 10 lb loads. The investigators thus concluded that factors that facilitated heat transfer and the sterilization of microbiological waste included the type of container in which the waste was placed, the physical characteristics of the load, and the autoclave bag. They also noted that the bag closest to the door heated more slowly than the middle and Pack bags and that the tops of bags must be adjusted to allow for the free passage of air and steam. The question was also raised as to the necessity of using a cycle (90 min) that will kill all the spores of the indicator, &. stearothermodhilus. Since those spores are much more heat resistant than the average organism it is unrealistic to require the elimination of all spores in order to render waste "non-infectious". Depending on the characteristics of the load, as already stated, spore forming bacteria other then 8. stearothermodhilus will be killed after 45 or 60 min. The use of microwave oven ir radiation as a method for sterilizing bacterial waste was reported by Latimer and Matsen. They undertook a quantitative study to determine the effect of timed microwave irradiation on commonly encountered laboratory bacteria, using an oven operating at 2,450 MHz. Organisms grown in broth culture and exposed to microwaves for 5 min included $. coli, E. plirabilis, E. aerueinosa, S. marcescenq, S. Bureus, S. edidermidig, and enterococcus. All organisms
were killed within the 5 min period. Spore strips containing viable E. stearothermodhilus spores were likewise exposed, with none surviving after a 5 min exposure. Loads of contaminated plastic petri dishes (about 100/load) exposed to the microwaves were rendered sterile within 5 min. The authors conclude that the utilization of microwave ovens for bacterial decontamination in laboratories is entirely feasible. It appears to be a practical time and energy saving method for the treatment of bacterial waste. The treatment of fungal, viral, and mycobacterial waste however, warrants additional investigation. Lastly, concern exists over the proper treatment of combined 'infectious/radioactive waste, Normally, the component representing the greatest hazard is addressed first, with the final disposal of the material subject to the regulations of the Nuclear Regulatory Commission (NRC). If the waste is considered "highly infectious" and is contaminated with low level radioisotopes, then extended autoclaving followed by storage for decay, or approved incineration (for solids), or autoclaving with release to the sanitary sewer (for liquids) may be utilized. In general, however, the time of storage for decay will result in the death of the infectious agent. The Centers for Disease Control (CDC) recommends treating radioactive blood and urine by chemical disinfection using sodium hypochlorite or hydrogen peroxide to inactivate the biological component prior to approved disposal. However, if chemical inactivation is not feasible, the waste should be steam-sterilized, tagged non-infectious, and disposed of according to the NRC.
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