By Eugene C. Cole, DrPH
From the June 2020 Issue
In the midst of the current coronavirus pandemic, building cleaning and sanitation practices have improved in quality and frequency, including the use of hospital-grade disinfectants in place of sanitizers. Since aerosol-applied disinfectant can reduce time and cost, questions have arisen about the effectiveness of disinfectants as gas or vapor-phase biocides. Does aerosol disinfection achieve the same or higher level of risk reduction as manual? Can it overcome substances such as soils and biofilms that may reduce effectiveness? Can it achieve the necessary dwell time to kill the microbes? As there is no selective exclusion as to where the aerosols land, is the integrity of some materials jeopardized? These and related issues are the focus of this article.
Cleaning And Manual Disinfection
Whether conducting routine business or dealing with the challenges of a pandemic, facility managers have a responsibility for ensuring a healthy indoor environment. The COVID-19 pandemic has emphasized the need for health-based cleaning, in particular, focused cleaning of high-contact touch points. This approach typically involves manual detergent cleaning followed by application of EPA-registered disinfectant.
Cleaning physically removes soils, microbes, and associated matrices in which they may be embedded. Cleaning is crucial. It removes substances that may interfere with the antimicrobial action of the biocide.
For use against COVID-19, disinfectant products have comprehensive microbiocidal claims. The EPA’s List N: Products with Emerging Viral Pathogens and Human Coronavirus claims for use against SARS-CoV-2, can be found on the agency’s website. COVID-19’s lipid envelope is susceptible to dissolution by detergents, contributing to the virus’s inactivation directly or by the actions of disinfectants.
The use of an EPA-registered disinfectant as an aerosol leads to three avenues of inquiry:
- Will it be effective in the absence of cleaning?
- Will it be as effective as manual application at inactivating microbial contamination if used following cleaning?
- Is there a rationale for its use both pre- and post-cleaning?
To answer these questions, it’s important to review the specifics of aerosol disinfection. That begins with terms and definitions. For our discussion, an aerosol is a collection of tiny particles or droplets suspended in air. The size and/or density of those particles typically have a bearing on terms used in aerosol disinfection. Common terms for treatment include gas-phase, vapor-phase, fogging (mists), and spraying.
Gas-Phase. Gases are formless fluids that expand to occupy the confines of a space or enclosure. They are so small that they are not visible. Air is our most common gas. When ultra-fine particles are introduced into air and also remain unseen, they are in gas-phase. Gas-phase ozone (O3) is an example. Ozone gas is recognized as a deodorizer in smoke damage restoration. But research has shown no meaningful effect of gas-phase ozone on either airborne or surface microorganisms.
Vapor-Phase. Vapor is the volatile, gas-phase form of a substance that exists in the liquid state at room temperature and pressure. As temperature and pressure change, the substance can be “vaporized” and mixed with air in various concentrations. The most common vapor-phase biocide used today is vaporized hydrogen peroxide (VHP). Studies demonstrate that effectiveness of vapor-phase disinfection is a function of both viral concentration and degree of soiling. The authors note that the results highlight the importance of effective cleaning prior to disinfection.
Fogging (Mists). Mists consist of droplets, typically less than 10 µm in size, dispersed in air. They are generated by breaking up a liquid into a dispersed state, such as by atomizing. When the mist is dense enough to affect visibility, it is called a fog. Fogging has long been used in the food processing industry to reduce microbial surface contamination and in agriculture to improve air quality. Fogging also has a history of use in infection-control.
Discussion of disinfectant fogging raises the question of its effectiveness compared to manual cleaning and disinfection. Fogging aims to kill microbial contamination where it lies. Manual cleaning and disinfection focuses on removal of the bulk of microbial contamination from surfaces prior to application of a chemical disinfectant to inactivate any remaining contamination.
This issue was addressed by the U.S. EPA. In April 2013, the Director of EPA’s Office of Pesticide Programs sent a letter to all EPA registrants of antimicrobial pesticide products that made claims to provide control of microorganisms when applied by fogging or misting. The letter explained EPA’s position that fogging/misting methods of application may not be adequate:
“Application by fogging/misting results in much smaller particle sizes, different surface coverage characteristics, and potentially reduced efficacy when compared to sanitization or disinfection product applications by spraying, sponging, wiping or mopping.
The absence of pre-cleaning in the presence of soil contamination, potential reaction with or absorption of the active ingredient for different surfaces, and humidity/temperature fluctuations can also impact distribution and efficacy of the product.
A surface treated by fogging/misting does not receive the same amount of active ingredient per unit area as the standard methods of application and, as a result, the level of efficacy actually achieved may not be the same level claimed on the label.”
Disinfectant fogging and manual cleaning and disinfection are both subject to human error, and neither approach eliminates all microbes. In general, fogging is quicker yet less effective. Manual cleaning and disinfection is more effective, yet slower and more costly.
Spraying. Spraying involves chemicals typically dissolved in water and dispersed under pressure as droplets greater than 10 µm. A pressurized can of aerosol spray disinfectant will deliver a very fine spray across surfaces. A pump or hand trigger sprayer will deliver larger droplet sizes.
A key question that arises in the use of all aerosol application methods: Will product deposition be sufficient to maximize microbial contact across all targeted surfaces, including penetration of all cracks and crevices that might harbor contamination? Historically, such thorough coverage could not be assured.
Electrostatic spraying (ES) seeks to address those issues. ES has been used in painting, agriculture, and the automotive industry for years, but it has not been extensively researched in regard to control of human pathogens. ES works like this: Fine droplets receive a positive charge just before they leave the nozzle of the sprayer. They are then attracted to negative or neutral-charged surfaces, and can literally wrap around them, providing a more even and consistent distribution.
While ES maximizes disinfectant distribution across horizontal and vertical surfaces, the question of efficacy in the absence of a precleaning step remains. This has been emphasized in recently presented but unpublished studies that have recommended the use of ES disinfection following routine cleaning and disinfection.
Cleaning. While manufacturers and contractors may tout their disinfectant products and services as stand-alone approaches to eliminate biocontamination, science continues to support cleaning. Clean is a condition free of unwanted matter, and cleaning is the process of achieving the clean condition. Thus, the removal of soils—including associated microbes—from high-contact surfaces remains the primary approach to achieve a healthy environment. If the process is carried out at an established frequency, the clean condition becomes easier to achieve.
Disinfection. If circumstances warrant—such as a bacterial outbreak in an indoor facility or a newly emerged virus in a global pandemic—application of an effective disinfectant following cleaning becomes essential. That application may be done manually or by a fogging or spraying process. Responsible cleaning and restoration contractors have the equipment, trained personnel, and expertise to respond effectively to a potential infectious agent situation. Protocols may vary. Some may do an initial fogging to provide a measure of protection for workers, then perform the manual cleaning followed by a post-cleaning application of disinfectant.
For many facility executives, issues regarding cleaning and disinfection in response to COVID-19 can be confusing, with product and service suppliers touting often conflicting claims. The answer is to be informed. Being armed with the following questions may be useful:
- What disinfectant(s) will be used? Are they on EPA’s List N? Are they incompatible with any materials? Are the products’ Safety Data Sheets (SDS) available?
- Will cleaning be conducted prior to disinfectant application? If so, how?
- What fogging, spraying, or electrostatic spraying apparatus will be used? What size droplets will be produced? How long will surfaces remain wet (dwell time) to achieve disinfection? Will disinfectant residue need to be removed? What odors will there be?
- What other projects and clients has this protocol been successfully used for? How often should this process be done to maximize results?
- Will a post-cleaning/disinfection evaluation be done to confirm effectiveness, such as with ATP testing? ATP testing is a process that utilizes metering devices to measure the amount of adenosine triphosphate (ATP)—an enzyme present in all organic matter—on surfaces before and after cleaning. ATP is considered a useful marker for cleaning effectiveness.
With a good working knowledge and understanding of building decontamination through cleaning and disinfection, facility executives and their teams will be prepared to ensure a healthy indoor environment for all.
Editor’s Note: An extended version of this article, “Aerosol Disinfection in a Pandemic World” is available for download in PDF form.
Dr. Cole, DrPH has enjoyed a long and distinguished career as a public health professional. Currently he is director of research for LRC Indoor Testing & Research in Cary, NC. Formerly he served as Professor of Environmental Health Sciences at Brigham Young University. Dr. Cole recently accepted a position on the executive committee of the Cleaning Industry Research Institute (CIRI). He has been a member of CIRI’s Science Advisory Council for several years.
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