Ongoing Evolution of Germicides: Accelerated Hydrogen Peroxide for Surface Disinfection
John A. Molinari, PhD
Many environmental surfaces in healthcare settings become contaminated with blood, saliva, exudate, and other biological matter during patient care. In dental facilities these include dental equipment, light handles, bracket trays, counter surfaces, reusable medical containers, and dental unit hose lines. When these items are contaminated with biological soil, infection control procedures require surface cleaning and disinfection, or disposable covers are to be used between patient appointments.1
Unfortunately, healthcare professionals can sometimes misinterpret these recommendations when performing routine infection control precautions. Misunderstanding of established principles and their clinical applications in such instances can ultimately result in misuse of otherwise acceptable surface disinfectant products and diminished effectiveness of the procedure.
This article will review aspects of environmental surface asepsis, examining the use of disinfectants in dentistry. First, pertinent, basic information concerning classification of inanimate surfaces will be presented, along with suggested criteria for disinfectant se- lection and Centers for Disease Control and Prevention (CDC) recommendations for cleaning and disinfection following patient care. Then, properties and clinical use of accelerated stabilized hydrogen peroxide formulations will be considered and compared with other classes of disinfectant germicides.
Environmental Surface Categories
Patient care items and surfaces contaminated during treatment present different degrees of infection transmission risk. The comprehensive 2003 CDC guidelines for infection control in dentistry1 delineated two categories of environmental surfaces: clinical con- tact surfaces and housekeeping surfaces. Recommendations differ for these two types of inanimate surfaces based on the potential for direct patient contact, degree, and frequency of hand contact, and potential surface contamination with body substances or pathogens.
Clinical contact surfaces are defined as surfaces that are frequently touched or that be- come contaminated and subsequently contact instruments, devices, hands, or gloves (eg, light handles, switches, chairside computers, countertops). They can act as reservoirs for microbial contaminants with the potential to transmit infection. Thus, the CDC recommends that these surfaces be covered with disposable, single-use barriers or cleaned and disinfected with a low- to intermediate- level disinfectant. The importance of cleaning cannot be overemphasized, and, therefore, the physical removal of debris is essential for successful subsequent disinfection procedures. In contrast, housekeeping surfaces (eg, floors, walls, sinks) have limited risk of disease transmission and can be decontaminated by cleaning on a routine basis.1,2
Criteria for Selection of Surface Disinfectants
A variety of Environmental Protection Agency (EPA) regulated and registered products are available as disinfectants. When considering which chemical class or product to use, it is beneficial to compare the efficacy of available agents with criteria for an ideal surface disinfectant (Table 1).3,4 Though a wide array of disinfectant formulations offer desirable characteristics, the perfect product exhibiting all of the desired criteria does not currently exist. Important considerations for a disinfectant’s efficacy include penetration and activity in the presence of bioburden, a broad antimicrobial spectrum, residual activity that becomes reactivated when surfaces are moistened, minimal toxicity, and compatibility with exposed surfaces. Both initial cleaning and disinfection are important because together they minimize potential cross-contamination.1
Manufacturers are also required to include instructions on the product label stating that disinfection is to be performed on pre- cleaned surfaces. Although separate cleaners and disinfectants may be used, chemicals that are able to penetrate and pre-clean surfaces contaminated with microbial-laden fluids prior to subsequent disinfection offer a more efficient approach by eliminating the need for a separate cleaning agent.4,5 Thus, a germicide that is able to penetrate and pre-clean surfaces contaminated with microbial-laden fluids prior to disinfection can eliminate the need for a separate cleaning agent.
Another important criterion entails antimicrobial treatment of contaminated surfaces; therefore, a desirable disinfectant should also be tuberculocidal and viricidal. Mycobacteria have among the highest levels of resistance of all microorganisms,4,6 and any germicide with a tuberculocidal claim is considered capable of inactivating a broad spectrum of pathogens, including less-resistant organisms such as blood- borne pathogens (eg, hepatitis B virus [HBV], hepatitis C virus [HCV], human immunodeficiency virus [HIV]). When a product is approved for tuberculocidal activity the product label should state that it kills Mycobacterium tuberculosis. The label should also mention that the use of the product on environmental surfaces plays no role in preventing the spread of tuberculosis, because M. tuberculosis is spread via aerosolized droplets and spatter. A kill claim for this organism on the label has been established as a benchmark for “intermediate-level disinfection,” whereby the germicide is registered by the EPA as a hospital disinfectant with the additional label claim of potency as tuberculocidal. Intermediate-level disinfection inactivates most vegetative bacteria, most fungi, and many viruses, but cannot be relied on to inactivate resistant microorganisms such as bacterial spores.
The relatively recent addition of “eco- friendly” into the safety property is aimed at addressing the issue of possible accumulation of chemicals on treated surfaces or in the environment as a result of disinfection procedures. Most available preparations do not meet this criterion; however, as disinfectant chemistry evolves, this issue is currently being addressed.
Available surface disinfectants contain either a single active chemical or combinations of antimicrobial agents. These include alcohols, quaternary ammonium compounds, sodium hypochlorite, phenolics, iodophors, and hydrogen peroxide. Each class of germicide has advantages and disadvantages for use.6 Some function as both good cleaners and broad-spectrum disinfectants, while others exhibit poor cleaning capability and may require initial cleaning with a water-based solution to accomplish intermediate-level disinfection. Others may also release an un- pleasant odor, stain surfaces, irritate tissues, or adversely affect treated fabric or metallic surfaces. Therefore, healthcare professionals should obtain as much pertinent information as possible before purchasing a surface disinfectant for routine use.
Hydrogen Peroxide-Based Germicides
Antimicrobials containing hydrogen peroxide have a long history of use in healthcare as disinfectants, antiseptics, and chemical sterilants. Historical studies showed that in addition to their antimicrobial activity they are safe for the environment and have low toxicity for treated tissues when used in low concentrations.7 This low molecular weight chemical can easily pass through cell walls/membranes to react with internal cell microbial components. It subsequently acts as an oxidant yielding high concentrations of antimicrobial hydroxyl radicals. As they accumulate in bacterial cells these anions are able to adversely affect multiple sites, such as DNA function, membrane permeability, and protein synthesis, leading to cell death. Hydrogen peroxide thus functions as a microbiocidal agent against a wide range of microorganisms.7,8
Another important characteristic is that during applications this oxidizing agent breaks down into water and oxygen, thus functioning as an antimicrobial while not releasing chemicals that can pose a possible risk to both users and the environment. Unfortunately, early formulations were unstable, yielding only low levels of the active chemical. They were also slow acting as antimicrobials.7 In an effort to build on the positive features of hydrogen peroxide activity, an accelerated hydrogen peroxide (AHP)-based surface disinfectant was developed and evaluated to address the weaknesses. This preparation is comprised of hydrogen peroxide; surfactants; wetting agents that reduce the surface tension of the liquid, allowing it to spread across or penetrate surfaces more easily; and chelating agents to help reduce metal content and/ or hardness of water. This highly stabilized form of hydrogen peroxide has been shown to exhibit an extended microbiocidal spectrum, along with a much more rapid cidal effect than peroxide alone.8,9 The most recent version of the agent is a 0.5% AHP surface disinfectant. (It should be noted that the hydrogen peroxide disinfectant being discussed in the following sections is EPA-registered as an intermediate- level disinfectant.)
Germicide Comparisons With Ideal Properties
Numerous chemical classes are available for environmental surface disinfection in health- care settings. As newer formulations are approved and become available for clinical use, it is important to evaluate their ability to fulfill key selection criteria. With specific reference to the present discussion, it is useful to assess how AHP compares with other representative agents. Four properties will be considered: cleaning capability; antimicrobial effective- ness; wetness; and safety for users, patients, and environment.
Initial cleaning is fundamental to infection control success and is routinely included in all published recommendations. It is defined6 as the removal of visible soil and debris, either manually or mechanically, that results in: (1) the reduction in the number of microorganisms; and (2) removal of organic matter, such as blood and tissue, and other debris that may interfere with sterilization and disinfection. Cleaning is the basic initial step before sterilization and disinfection. Without it the presence of organic debris on instruments, devices, and other items can interfere with microbial inactivation.
Aqueous-based germicidal agents can effectively clean surfaces prior to disinfection. The physical action of scrubbing with detergents and surfactants and rinsing with water removes large numbers of microorganisms from surfaces. As a water-based germicide, AHP has been proven to also be an excellent cleaner for removal of bioburden prior to disinfection.7
For germicides that contain alcohols there can be issues with regard to cleaning. Alcohols exert their microbiocidal effects by denaturing and dehydrating proteins. A number of surface disinfectants are available that contain alcohols ranging in concentrations from low (below 10%) to high (79%). Those with a low concentration of alcohol can still be considered aqueous-based germicides and retain the capability to remove debris. Exposure of soiled items and surfaces to higher alcohol concentrations, however, can inhibit cleaning by rendering denatured and dehydrated proteinaceous material insoluble and tenaciously adherent to most surfaces. This coating of denatured bioburden can protect contaminant microorganisms from the killing effects of alcohols for prolonged periods. Coupled with rapid evaporation from treated environmental surfaces, alcohols can have limited activity on protein-coated bacteria viruses generated during patient care. As such they are not regarded as effective surface cleansing agents despite having a relatively broad antimicrobial spectrum of activity.10
2. Kill Claims for Healthcare Pathogens
The EPA requires that disinfectants list specific contact times to accomplish disinfection. The length of kill time to achieve cidal activity is dependent on both the antimicrobial proper- ties of the germicide and the resistance of target bacteria and viruses. This requirement can vary from as little as 1 minute to up to a 10-minute exposure interval for effective disinfection. When considering property Nos. 2 through 4 in Table 1, it becomes readily apparent that a disinfectant with a very short contact time for microbiocidal activity can provide good assurance that common healthcare pathogens are being killed before the liquid can dry or be removed, and also before individuals would likely retouch the surface.4 A short (ie, 1 minute) contact time also promotes better opportunity for disinfectant compliance. In contrast, when personnel in clinical settings were observed using disinfectants that called for a 10-minute contact time, it was noted that they frequently left the solution on surfaces for only a portion of that interval.4
Improvements have been made in this regard with germicide classes, although certain phenolic and quaternary ammonium disinfectants historically cited a 5- to 10-minute exposure time for maximum effectiveness. Later generations of these surface disinfectant classes, however, have been formulated to demonstrate considerably shorter kill times (ie, 2 to 3 minutes) for disinfection. With regard to the 0.5% AHP disinfectant preparation, the 1-minute contact interval for killing M. tuberculosis, as well as for non- enveloped viruses (ie, poliovirus, norovirus, rotavirus), enveloped viruses (ie, HBV, HCV, HIV, influenza virus), and common bacterial hospital pathogens (ie, methicillin-resistant Staphylococcus aureus [MRSA], vancomycin- resistant Enterococcus [VRE], Escherichia coli, Pseudomonas aeruginosa, Salmonella choler- aesuis), allows the germicide to meet the three important criteria from Table 1 cited above.10
AHP’s rapid 1-minute antimicrobial action on surfaces was also noted by dental personnel as a reason for better compliance.11
The EPA requires a disinfectant to remain in contact with target microorganisms long enough to meet kill times stated on the label. Otherwise, if germicidal liquid dries on surfaces too quickly, effective cidal activity may not occur. Ideally, a disinfectant should be able to keep surfaces wet with a contact time that is at least, if not greater than, the listed kill times.4,12
In addition, being able to use a single application of the product to provide sufficient active liquid to meet kill criteria would be advantageous. As expected, a preparation’s chemical composition plays a major role in determining wetness. Aqueous-based products, such as quaternary ammoniums, iodophors, sodium hypochorite, phenolics, and hydrogen peroxide, keep surfaces wet longer than alcohol- based solutions.13 Depending on individual contact times and the size of the surface area, these types of products can meet stated activity claims for certain kill times. In contrast, alcohol-based formulations can evaporate rapidly on environmental surfaces before contact times may have been reached. When coupled with alcohol’s diminished cleaning ability mentioned above, protein-coated pathogens may not be adequately exposed to the antimicrobial.
With reference to AHP disinfectants, labora- tory studies have indicated that disinfectant wipes comprised of 0.5% AHP outperformed other disinfectant wipes containing either a phenolic or varying alcohol concentrations. AHP test wipes were able to keep treated surfaces wet for the recommended 1-minute contact time, while, in contrast, wipes con- taining the other chemical agents dried before prescribed kill times.14,15
4. Tissue and Environmental Safety
Chemical cleaners, disinfectants, and sterilants can be used many times a day in health- care facilities. Unfortunately, in addition to their established infection control roles, many cleaners and/or germicides also can present health and environmental chemical hazards. Common toxicity problems for humans vary from acute irritation of mucous membranes and eyes and damage to keratinized epithelium, to chronic toxicity from repeated chemical exposure over prolonged intervals. By reducing or eliminating harmful chemicals as much as possible, personnel health concerns can be lessened without compromising infection control standards. For example, glutaraldehydes were previously used in many dental and medical facilities as chemical sterilants and high-level disinfectants. Unfortunately, this class of chemical also damages many materials and is irritating and allergenic to tissues. Repeated exposure to this aldehyde can cause acute and chronic tissue problems, including breathing difficulties, hives, head- aches, nausea, and dizziness. Alternative approaches have been successfully implemented to replace this hazardous chemical with more heat-stable devices and single-use, disposable items in healthcare settings, and, subsequently, glutaraldehyde use as an infection control agent has declined dramatically.
Healthcare personnel have also experienced irritation of tissues and respiratory complications after repeated exposure to other germicide classes, including products containing quaternary ammonium compounds, sodium hypochlorite, and synthetic phenolics. In contrast, the safety of AHP during prolonged use has been evaluated and documented.8 The EPA has assigned this type of hydrogen peroxide a Category 4 for skin and eye irritation, its lowest toxicity level. In fact, the Safety Data Sheet for the 0.5% AHP surface disinfectant states, “The product contains no substances which at their given concentration are considered to be hazardous to health.”
Environmental accumulation and contamination of air, water sources, and soil are also concerns with chemical germicides. Many state and local governments regulate certain chemicals to protect the environment, with regulations aimed at limiting chemical disposal into waste systems and preventing accumulation of potentially harmful chemicals in the environment.15 In that vein, AHP is an eco-friendly disinfectant, because the active agent releases only water and oxygen during use. Thus, it does not lead to any accumulation of chemical residue either on exposed surfaces or in the environment.
A variety of clinic contact surfaces are found in healthcare facilities. In dentistry these include countertops, light handles, chair buttons, and unit controls. While it is not necessary to sterilize these items, cleaning and disinfection procedures should be used to decontaminate these potential sources of cross-infection. A thorough cleaning followed by appropriate disinfection according to manufacturer instructions can provide effective environmental surface reprocessing. Although science has not yet yielded the ideal chemical germicide that meets all criteria included in the present discussion, progress continues toward that goal. This is evidenced by the properties exhibited with a newer generation of stabilized, accelerated hydrogen peroxide, which com- pare favorably with features of many other available disinfectant chemical classes.
About the Author
John A. Molinari, PhD
Director of Infection Control
The Dental Advisor
Ann Arbor, Michigan
University of Detroit Mercy School of Dentistry
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